1

AR-7868

B.Sc. (Hon’s) (Fourth Semester) Examination, 2013

BIOTECHNOLOGY (Botany-I : Plant Physiology)

A. Select one correct option for each of the following questions: (10 x 1)

1. Macronutrients are:-

a. Carbon, Hydrogen, oxygen

2. Micronutrient is:-

d. Zinc

3. Photosynthesis take place normally by-

a. Chloroplast

4. In addition to plant, photosynthesis take place in-

c. Bacteria

5. Number of carbon in pyruvic acid is-

b. 3

6. Glycolysis occurs in –

b. Cytoplasm

7. Nitrogen fixation help to plant for growth-

a. Yes

8. Nif genes produce a special enzyme complex called-

a. Nitrogenase

9. The important worker in the field of vernalization:-

c. Klippart

10. IAA is :-

a. Plant hormone

2

Descriptive Type Question

Q : 01 Describe essential micronutrients and symptoms of their

Deficiency in plant

Answer: In general it may be stated that the micronutrients and a few of the

macronutrinets play their Part by participating in enzyme systems. It is believe that that

there are two basic ways in which this may be brought about. Micronutrients like copper

and molybdenum and the macronutrient iron act as electron carriers by virtue of valency

changes. The other important method by which micronutrient (and also the

macronutrient, magnesium) act by combining with the enzyme-substrate complex. The

role of the micro-nutrient elements is given below:

MANGANESE

Functions of Manganese

Primarily manganese functions as an enzyme activator in several reactions of

respiration and nitrogen metabolism.. Manganese also plays some role in the

synthesis of chlorophyll and in the transfer of electron from H2O to photoxidized

chlorophyll in photosynthesis (Homann, 1967).

Manganese Deficiency Symptoms

Manganese deficiency also causes chlorosis which is distinct from that of

manganese or iron deficiency. That leaf takes a mottled appearance. The

chloroplasts lose chlorophyll and starch grains and become yellow-green in

colour. They become vacuolated and granular and finally disintegrate.

BORON

Function of Boron Boron differs from the other micronutrients in that there is no evidence to suggest

its connection with the enzyme systems and it also differs in that is absorbed as an

anion, i.e., borate or tetra borate, rather than as a action like the other metabolism

have been suggested, it function in the translocation of sugar is the only one,

which has been accepted by all. It is believed that boron facilitates the

translocation of sugars in plants. It has been that place of high metabolic activity

in a plant requiring high quantities of sugar, are the first to be affected in the

absence of boron.

Boron Deficiency Symptoms

Boron deficiency results in the death of shoot tip. The root tips die and the shoot

growth is stunted. Flowers are not formed. The leaves have a coppery texture.

Internally, carbohydrates and amino acids accumulate.

Boron deficiency tends to shift metabolism from glycolysis to pentose phosphate

pathway.

Physiological diseases like internal cork of apples, top root of tobacco, cracked

stem of celery, browing of cauliflower and heart root of sugarbeet are developed

as a result of boron deficiency.

3

COPPER Function of Copper

The element is required in very small quantity. IT is very toxic, when present in

large in larger quantity. It acts as a catalyst in oxidation reduction reaxtions, since

it is a constituents of certain oxidizing and reducing enzymes. It is a component

of ascorbic acid and polyphenol oxidase. It is a part of plastocyanin and thus may

function in electron transport chain of photosynthesis.

Copper Deficiency Symptoms

Copper deficiency causes some physiological diseases, e.g., dieback disease of

citrus and ‘reclamation’ disease of cereal and leguminous plants. ,, ZINC

Function of zinc

Zinc function as the activator of certain enzymes , e.g., carbonic anhydrase

,alcohol dehydrogenase, hexokinase, etc. Zinc is the essential for the biosynthesis

of the plant auxin, indole-3,acetic acid. The element is also believed to be

concerned with protein metabolism.

Zinc Deficiency Symptoms

Zinc deficiency causes reduced stem growth due to increased synthesis of auxin.It

results stunted vegetative growth and distorted leaves.Chlorosis is the interveinal

region of the leaves is another effect of the elements deficiency. The internodes

reduced in the size and the effect is the sometimes referred to as ‘ litter leaf

disease’ other deficiency diseases are rosettes of pecan, white bud of maize,

mottle leaf disease of apples and walnut. The absence of zinc also suppresses

seed formation end causes malformation in fruiting trees.

MOLYBDENUM

Functions of Molybdenum Molybdenum is required in very little quantity by the plants. The main role of

molybdenum in plants has been found to be in the nitrogen metabolism. It acts as

an activator for the aenzyme nitrate reductase.

Molybdenum deficiency symptoms Its deficiency results first in the chlorotics interveinal mottling of the lower

leaves. It also inhibits the flower formation. Whip-tail disease of cauliflower has

been reported to be due to deficiency of the element.

CHLORINE

Function of Chlorine

Recently chlorine ion (Cl-) has been shown to be the essential in a number plant

species in small but definite amount for their health growth. Vernon and Ke (

1966) believed that chlorine ions are essential in the transfer of electron from

H2O to photo-oxidized chlorophyll in photosynthesis.

4

Chlorine Deficiency Symptoms

Due to chlorine deficiency plant show poor growth the root are slinted and leaves

and poorly developed. The leaves shown chlorosis as well as nerosis.

____________

5

Q : 2 Describe Difference between C3 and C4 Plants

Answer :

Difference between C3 and C4 Plants

C3 Plants(Calvin cycle) C4 Plants(Hatch and Slack cycle)

1. Calvin cycle is found in all

photosynthetic plants.

1. C4 cycle is found in certain

tropical plants.

2. The efficiency of CO2 absorption at

low concentration is far less. So they

are less efficient.

2. The efficiency of CO2 absorption at low

concentration is quite high. So they are

more efficient plants.

3. The CO2 acceptor is Ribulose-1,5-

diphosphate.

3. The CO2 acceptor is phosphoenol

pyruvate.

4. The first stable product is

phosphoglyceric acid.

4. Oxaloacetate is the first stable product.

5. All cells participating in photosynthesis

have one type of chloroplast

(monomorphic type).

5. The chloroplast of parenchymatous

bundle sheath is different from that of

mesophyll cells (dimorphic type). The

chloroplasts in bundle sheath cells are

centripetally arranged and lack grana.

Leaves shown Kranz type of anatomy.

6. In each chloroplast, two pigment

system ( Photo system I and II) are

present.

6. In the chloroplast of bundle sheath

cells, the photo system II is absent.

Therefore, these are dependent on

mesophyll chloroplasts for the supply

of NADP+ H+.

7. The calvin cycle enzymes are present

in mesophyll chloroplast. Thus, the

Calvin cycle occurs.

7. The Calvin cycle enzymes are absent

in mesophyll chloroplasts. The cycle

occurs only in the chloroplasts of

bundle sheath cells.

6

8. The CO2 compensation point is 50-150

ppm CO2.

8. The CO2 compensation point is 0-10

ppm CO2.

9. Photorespiration is present and easily

detectable.

9. Photorespiration is present only to a

slight degree or absent.

10. The CO2 concentration inside the leaf

remains high (about 200 ppm).

10. The CO2 concentration inside the leaf

remains low (about 100 ppm).

11. The 13C /12C ratio in C- containing

compounds remains relatively low

(both 13CO2 and 12CO2 are present in

air).

11. The ratio is relatively high, i.e., C4

plants are more enriched with 13C

than c3 plants.

12. Net rate of photosynthesis in

full sunlight (10,000-12,000 ft.c.)

is 15-25 mg of CO2 per dm2 of leaf

area per h.

12. It is 40-80 mg of CO2 per dm2 of leaf

area per h. That is, photosynthesis rate

is quite high. The plants are efficient.

13. The saturation intensity reaches the

range of 1000-4000 ft. c.

13. It is difficult to reach saturation even

in full sunlight.

14. Bundle sheath cells are unspecialized. 14. Bundle sheath cells are highly

developed with unusual construction

of organelles.

15. Only C3 cycle is found. 15. both 4 and C3 cycles are found.

16. The optimum temperature for the

process is 10-250C.

16. In these plants, it is 30-450C. So these

are warm climate plants. At this

temperature, the rate of

photosynthesis is double than that of

C3 plants.

17. Oxygen present in air(=21%O2

)markedly inhibits the photosynthesis

process as compared to an external

atmosphere containing no oxygen.

18. For synthesis of one glucose

molecule 18 ATP are required.

17. The process of photosynthesis is not

inhibited in air as compared to an

external atmosphere containing no

oxygen.

18. In this process, 30 ATP are required

for the synthesis of one glucose

molecule.

7

Q : 3. FACTORS AFFECTING THE RATE OF RESPIRATION Answser : The rate of respiration varies with a number of factors, both external as well as internal

Normalh the rate of respiration would increase with increase in respirable material or

oxygen. However, there are many cases where oxygen reduces the rate of sugar

breakdov-r. and even conserves it. This is known as the Pasteur effect.

There are a number of factors, some internal, others external which influence the rate of

aerobic respiration. The internal factors are the protoplasmic factors and the

concentration of the respirable material. The external factors are temperature, light,

oxygen concentration, COa concentration, water, injury, mechanical effects and effects of

certain chemicals.

INTERNAL FACTORS

(1) Protoplasmic Factorsr

The rate of respiration depends upon the quantity of the protoplasm. This is why young,

meristematic tissues which are relatively rich in protoplasm, usually have higher rates of

respiration than older tissues in which the proportion of cell walls and the vacuoles is

greater.

(2) Concentration of the Respirable Material

The amount of the soluble substrate present is an important factor in controlling the rate

of respiration. If other factors are not limiting, the rate of respiration will increase with

increase in the concentration of the respirable material.

EXTERNAL FACTORS

(3) Temperature

The rate of respiration is very much affected by temperature. In the temperature

range between 0° and 45° C, a rise in temperature causes a marked increase in the rate of

respiration. In many experiments the process has been found to follow vant Hoff 's law

i.e., the respiration rate increases two or three times for every rise of 10°C. The optimum

8

temperature of respiration is near about 30°C. Beyond this temperature, the increase in

the rate is not maintained for long.

(4) Light

While some workers like Emerson and Lewis (1943) and Jhonston (1944) have found

direct enhancing effect of light on respiration, most of the effects of light on respiration

are indirect in nature. Light for example, brings about photosynthesis and thus increases

the amount of respirabie material. Light also affects respiration by increasing the

temperature of the respiring organ.

(5) Oxygen Concentration of the Atmosphere.

Oxygen is absolutely indispensable for the aerobic type of respiration. Its percentage in

the atmosphere remains constant. Considerable changes in the concentration of oxygen in

experiments have been found to be ineffective in increasing or decreasing the rate of

respiration.

(6) Carbon Dioxide Concentration

The concentration of CO,, is atmosphere is almost constant and is, therefore, not likely to

affect the respiration rate of the plants to any appreciable extent. In the soil, however, the

concentration of CO2 is very much variable.

(7) Water

In the case of a well-hydrated plant the rate of respiration is not likely to be affected

much by slight changes in the content of water. Shortage of water, however, does

increase the rate of respiration. It is believed that in wilted tissues the accumulated starch

gets converted into sugars and, therefore, an increase in the respiration rate takes places.

(8) Injury

Workers like Hopkins (1927) and others have shown, that whenever a plant tissue is

wounded the sugar content of the wounded portion is suddenly increased. This increase in

the sugar content is believed to be responsible for the observed temporary increase in the

respiration rate.

9

(9) Mechanical Effect

A purely mechanical stimulation of respiration has been demonstrated in the leaves of a

number of species by Audus (1939,40,46). A Gentle rubbing or bending of the leaf blade

was sufficient to induce a marked rise in the respiration rate (20% to 183%) which

persisted for several days. If the treatment was repeated at inverval, the stimulus

gradually lost its effect in increasing the rate of respiration. No satisfactory expiation has

been put forward for this mechanical stimulus.

____________

10

Q : 4 Describe Nitrogen cycle.

Answer :

NITROGEN CYCLE

Introduction

Nitrogen constitutes 78% of the atmosphere .

This gas can not be utilized by the higher plants in the Free State.

A number of micro-organisms and blue green algae are however, capabl of fixing the

atmospheric nitrogen in the form of compounds. Nitrogen is also fixed by lightning and

rainfall.

The nitrogen cycle can be studied under four convenient headings

(1) Nitrogen fixation

(2) Ammonification ,

(3) Nitrification

(4) Denitrification.

Ammonification

Plants synthesise organic nitrogenous compounds with the help of the nitrogen

pool of the soil . In leguminous and certain non-leguminous plants atmospheric

nitrogen can also be fixed up indirectly. Animals derive their nitrogen

requirement from the plants When the plants and animals die , their protein

contents are decomposed in to ammonia by a variety of micro- organism. The

bacteria which bring about protein decomposition are termed ammonifying

bacteria eg. Bacillus ramosus,B. vulgaris and B.mycoides. Ammoniais added to

the nitrogen pool of the soil or to water (in the form of soluble ammonium

compounds). Some of the ammonia goes out in to the atmosphere . Ammonia can

be directly taken up by the plants or can be converted to nitrates by the process of

nitrification.

11

Nitrification

Ammonia or the Ammonium compounds formed by ammonification are

converted in to nitrite and then in to nitrate by a group of bacteria called nitrifying

bacteria. Ammonia is oxidized to nitrate by Nitrosomonas and nitrite is further

oxidized by Nitrobacter.

Nitrosomonas

2NH3 + + 3O2------------ 2NO2+ 2H2 + 2H2O

2NO3- +O2 -------------2NO3 + energy

Once nitrate is formed it is taken up by the plants in which it gives rise to ammonia.

Denitrification

A group of bacteria called denitrifying bacteria ( Bacillus denitrifications) break

up nitrates, and ammonium compounds in to molecular nitrogen (N2) which is

released in to the atmosphere . Such bacteria are thus responsible for reducing the

nitrogen content and therefore, the fertility of the soil. It should be noted that loss

of nitrogen in to the biosphere due to denitrification and sedimentation (in

aquatic ecosystems ) is more than compensated by gains by nitrogen fixation,

nitrification , volcanic release of ammonia , oxidation of atmospheric nitrogen

by lightning and the weathering of the rocks.

Loss of nitrogenous compounds in the form of cereal grains , straw , hay etc. or

harvested underground storage organs, etc. are compensated by the addition of

natural manure and artificial fertilizers in the soil. In agriculture crop rotation

involving a leguminous crop is often practiced to maintain the pool of available

nitrogen in the soil.

Finally, it should be clear that the nitrogen cycle involves a vast number of

organisms (almost the whole plant and animal kingdom) and a variety of

pathways. This is no single nitrogen cycle. There is a group of cycles all

interacting with each other.

12

Nitrogen Cycle

13

Q : 5 Describe the structure of Enzymes.

Introduction

The history of enzymes began with the work of Dubrunfaut (1830) who prepared malt

extract from germinating barely seeds. Payen and Persoz 1833) extracted the enzyme,

diastase, from the malt extract. Louis Pasteur (1857) demonstrated that the living yeast

cells were responsible for alcoholic fermentation. Pasteur used the term "ferments" for

such biocatalysts. Thus two types of ferments or catalysts were distinguished:

unorganized ferments (like diastase, etc.) and organized ferments (like living etc.). The

term enzyme was later proposed by F.W. Kuhne (1978) for non-living unorganized

ferments. .

The modem era in study of the enzymes began when Buchner (1897) accidentally

discovered that even a juice extracted from yeast cell brought about fermentation of sugar

like that of the living yeast cells.

Broadly, enzymes carry out two important functions in a living organism. They

are able to accelerate or retard or bring about chemical reactions. By virute of their

specificity they are able to regulate a number of different reactions at the same time.

STRUCTURE OF ENZYMES

There are certain enzymes which have only protein, while proteins of majority of

the enzymes have an attached nonprotein group. The protein part is called apoenzyme

whereas the non-protein part is called the co-factor. The complete enzyme is called

holoenzyme or conjugated protein In such cases, neither the apoenzyme nor the co-factor

is capable of functioning catalytically, if the are not in a combined form. It must be borne

in mind that the co-factor may be identical in several enzymes and, therefore, the nature

of the reactions will be identical. The particular substrate actec upon by an enzyme is

selected by the protein part of the enzyme.

The cofactor is broadly classified into two types : prosthetic group or co-enzyme. The

firmly bonded cofactors are called prosthetic groups and the loosely bonded organic

cofactors are called coenzymes. When functions as prosthetic group, it is generally

referred to as an activator. The metal activators have been found to be directly concerned

with the catalytic properties of some of the enzymes. The metal's separation from the

14

aponenzyme makes the latter completely inactive. Many workers believe that the

activator may help in the binding of a substrate to its enzyme. Some of the activators are

copper, iron, manganese, magnesium, zinc and molybdenum. In the case of iror the metal

is sometimes also present in the form of he me, or in form of some complex organic

molecules with an iron centre such as iron porphyrin.

Diagram showing the protein and non-protein part of an enzyme.

In contrast to the metal-requiring enzymes, there are enzymes which require certain

complex organic substances as their co-factors. These organic prosthetic groups are

loosely attached to the protein part and are called coenzymes. These groups act as donors

or acceptors or groups of atoms that have been added to or are removed from the

substrate. Some of the coenzymes are nicotinamide-adenine-dinucleotide (NAD+),

nicotinamide-adenine-dinucleotide phosphate (NADP+), adenosine triphosphate (ATP),

coenzyme A (CoA), flavin mononucleotide (FMN), and flavin adenine dinucleotide

(FAD). Besides, vitamins are now known to function as coenzymes. The vitamins of the

B-complex including thiamine (vit. B), riboflavin (vit B,), pyridoxine (vit B6), niacin,

pantothenic acid, biotin, and adenine, all constitute prosthetic groups or portions of the

prosthetic groups.

Endo-enzymes and Exo-enzymes. Enzymes which act within the cells in which they are

synthesised are called endoenzymes to differentiate them from exoenzymes which act

outside the cells of their origin. Most of the enzymes included in the first type are known

15

as hydrolysing enzymes while those of the second type are known as desmolysing

enzymes.

Sometimes instead of enzymes their precursors (which are inactive) are present in the

cells. Such substances are termed proenzymes or zymogens. Most of the digestive

enzymes like pepsin, trypsin and chymotrypsin arise from these inactive zymogens.

Zymogens are converted into enzymes with the help of some compounds called kinases.

The exact mechanism of this conversion is not definitely known. Perhaps one or more of

the peptide bonds are removed during the conversion. Some believe that the zymogens

are prosthetic groups of enzymes.

Examples of metals requiring enzymes are listed in Table

Some enzymes requiring metal activators.

Metals

Magnesium Phosphatases. kinases

Copper Tyrosinase, respiratory proteins of invertebrate animals.

Zinc Various dehydrogenases, peptidases, carbonic anhydrase.

Iron Cytochromes, haemoglobin, electron transport system in

mitochondria.

Manganese Peptidases, some enzymes of the nitric acid cycle.

Cobalt Peptidases, in vitamin B(,.

Molybdenum Nitrate reductase, xanthine oxidase, nitrogenase

Potassium Phosphopyruvate transphosphorylase, f'ructokinase

Calcium Actomyosin.

A list of some important coenzymes Coenzymes

1. Hydrogen-transferring Coenzymes

2. Group-transferring Coenzymes

3. Coenzymes of isomerases and lyases

16

Relative Distribution of Enzymes and Prosthetic Groups. (From M.H. Smith, 1967)

Enzyme

Number of

Pyridoxal

Flavin

Metal

Heine

Thiamme

Biotin

Cobal-

enzymes

pyroph-

amine

known

osphate

I Oxidoreductases

222

1

34

24

9

2

0

0

II Transfcrases

238

18

0

0

0

1

1

0

III Hydrolascs

213

21

0

4

0

0

0

0

IV Lyases

117

9

1

1

0

4

0

1

V Isomerases

47

4

0

0

0

0

0

1

VI Ligases

47

0

0

0

0

0

4

0

Total

884

53

35

29

9

7

5

2

A list of some important coenzymes and prosthetic groups is given in together with a

brief account of their function. Coenzymes generally contain a vitamin sub-unit which

probably accounts for the essential role of vitamins in animal diets. Shows the relative

distribution of enzymes and their prosthetic groups.

17

Question : 06 Describe Abcisic acid

Answer

Certain plants have found to contain a new type of harmone which acts as growth

inhibitor.It has a wide range of physiological effects-promoting senescence and

abscission, retardation and inhibiton of growth.

Hemberg (1949) showed that extract of dormant potato tubers and buds of ash (Fraxinus

excelsior) contain substances which inhibit the growth of the Avena coleoptiles and the

removal of dormancy of the tubers resulted in marked reduction in the level of the

inhibitors.Osborne (1955) was the first to provide evidence for the occurrence of a

growth inhibiting substance in plants . She demonstrated that an extract of ageing leaves

caused premature drooping of young leaves of bean plant.

Robinson et al (1963) and Robinson and Wareing (1964) succeeded in extracting the

inhibitory substance and called it dormin (because it also caused dormancy ). Addicott

and his co-workers also extracted a substance from young cotton fruits ( cotton has large

scale abscission). Okhuma etal. (1963,1965) iaolated a very active inhibitor from young

cotton fruits and called it abscisin II. It was later on realized that both dormin and

abscisin II were the same thing and the substance was named abscisic acid (ABA).

Abscisic acid is naturally occurring harmone present in a wide variety of plants . Pure

ABA gives good Avena coleoptile test and other growth test to show that it is highly

active growth inhibitor ( at less 1 ppm)

ABA has been found to be synthesized in all the cells containing chloroplasts or

amyloplasts. According to Milborrow (1984) ABA is present throughout the plant. ABA

ias abundant in vascular plant . ABA is translocated mainly through phloem and

xylem.Xanthophyll is believed tpo be the the main intermediate compound in the

synthesis of ABA . The concentration of ABA is maximum during Embryo genisis .

18

Physiological roles of ABA

1. It regulates the dormancy of buds and seeds probably by in hibiting the growth

process . Since gibberellin delays or prevents the onset of dormancy it is possible

that bud dormancy is regulated by a balance between gibberellin and ABA.

2. ABA accelerates the senescence of leaves . The effect can , however , be reserved

by cytokinins in duck weed (Lemna).

3. ABA inhibits germination of seeds such as those of lettuce but this can be

reversed by kinetin .

4. It inhibits gibberellin – stimulated growth in various tests . It is believed to act as

a specific antagonist to gibberellic acid , and is therefore termed “anti-

gibberellin”.

5. ABA inhibits gibberellin-induced alpha amylase formation in barely aleurone

(Chrispeels and Varner , 1967 ).

6. It causes ageing and abscission of leaves.

7. It promotes root growth but inhibits shoot growth .It regulates gene expression.

8. ABA has been found to accumulate in high concentration in leaves which are

wilting. This increased production of ABA by the leaves is correlated with

stomatal clouser. Treatment with ABA has been demonstrated to result in

stomatal closure in as short as 5 minutes in normal leaves. It is believed that

ABA interferes with the uptake or retention of potassium (or sodium) ions in

guard cells.

Mode of Action of Abscisic Acid

ABA is believed to act in the following manner:

i) It may compete with auxins, gibberellins or cytokinins for specific enzyme

site since it is known to be antagonisitic to their effects.

ii) It may inhibit the biosynthesis of other growth harmones or even inactivate

them.

iii) ABA may inhibit RNA and protein senthesis.

iv) It may stimulate the production of certain hydrolytic enzymes.

19

Q; 7 Discuss photoperidism

Answer :-

Photoperiodism About eighty five years ago, two workers in the U.S. Department of Agriculture - W. W. Garner

and H.A.A Il ard found that a newly developed tobacco mutant, Maryland Mammoth, and

soybeans (Glycine max) had strange seasonal pattern of flowering. The former would grow very

well during summer but would not flower at all. The same variety would, however, show excellent flowering and fruiting when grown during the winter season. Soybeans would similarly

flower only in the late summer irrespective of the time of sowing in the previous spring. They

studied the effect of different temperature, nutrition and soil moisture on these plants but none of these was found to regulate the flowering. When they placed the plants in a dark chamber and

gave a shorter daily light period reduced in length by few hours flowering occurred. They,

therefore, examined a number of species under different conditions of daylength by either

reducing the natural daylength in summer or increasing the same during winter by artificial illumination.

Garner and Allard (1920) suggested the term photoperiodism to designate the response:

organisms to the relative length of the day and night and photoperiod to designate the favorer.

length of day for each plant. They classified the plants into three groups according to their

photoperidism.

(a) Short-day plants (b) Long-day

(c) Day-neutral plants

Photoperidism

20

Short-day plants flower when the day length is less than a certain critical length say twelve"

hours. In other words the day length must not exceed a critical value, if they are to flower.

Long-day plants flower when the day length is greater than a certain critical length, say twelve

hours. In other words the day length must not be less than a certain critical value.

While most of the flowering plants fall into three major categories : short day plants, long c; plants and photo neutrals there are some other types in which the photoperiod requirement is

subjects; to environmental factors such as temperature. There are plants which have a qualitative

photoperiod requirement at one temperature but a quantitative requirement at another temperature. Besides there are intermediate day-length plants and ambi-photoperiodic plants. " ~ * "•*_ - - "

SHORT DAY PLANTS

(LONG NIGHT PLANTS)

Short day plants are mostly found in the tropics where the length of the day never

exceeds more than 14 hours even in the summer season. In temperate zone the plants

flower in the late summer season when the length of day had decreased.

. There are three categories of short day plants: (i) Qualitative Short Day Plants (ii) Quantitative Short Day Plants (iii) Short-Long Day Plants (SLD)

The salient features of the short-day plants are as follows:-

a) Flowering is inhibited if a very weak intensity of light is given to the plant for

some time during the dark period.

b) The flowering is also suppressed, if the dark period is interrupted midway by even

a single flash of light. The intensity of light needed to inhibit flowering in such a

case is quite low. The interruption of the dark period is not very effective, if it is

near the beginning or the end of the dark period.

c) Short day plants unlike the long day plants are incapable of flowering under

alternating cycles of short dark and short light periods.

d) Several short-day plants flower in continuous darkness, if they are given sucrose

(Hillman, 1959) suggesting that light is needed only for the photosynthesis of

food material.

21

Flowering in a short day plant is suppressed by very low intensities of light

as well as by even a simple flash of light during the long dark period.

All this leads to the conclusion that it is the length of the night and its continuity that are

really important in initiating flowering in short-day plants. The short-day plants may,

thus, also be called long night plants.

Under long day conditions also flowering can be induced if the dark period is increased

by transferring the plant to darkness for some time after or before the night period.

Some of the examples of short-day plants are Tobacco (Nicotiana tabacum), Soybean,

Fragaria (Strawberry), Coffee (Coffeea arabica), Rice (Oryza saliva), Bryophylium

(Bryophyllum pinnatum), Chrysanthemum (Chrysanthemum spp.}, Cocklebur (Xanthium

strumarium), Cosmos (Cosmos sulphureus), Goosefoot (Chenopodium rubrum),

Japanesse morning glory (Pharbitis nil), Kalanchoe (Kalanchoe blossfeldiana). Morning

glory (Ipomoea purpurea), Poinsettia (Euphorbia piilcherrima), Violet (Viola

papilionancea), etc.

LONG-DAY PLANTS

There are three categories of long day plants

(i) Qualitative Long Day Plants (ii) Quantitative Long Day Plants (iii) Long- Short Day Plants (SLD)

Long-day plants have the following essential features: Long-day plants require a

photoperiod of more than a critical length. The critical length varies from 4 to over 18

hours for such plants. They require either a relatively small period of darkness or no

darkness at all. This is supported by the fact that long-day plants usually flower best in

continuous light.

a) In long-day plants, periods of darkness have an inhibitory effect on the flowering

of the plants. A long-day plant can be made to flower even under short-day

conditions, if a flash of light is given to the plant during long dark period.

22

b) Another interesting point regarding the long-day plants is their capability to

flower in short photoperiods, provided these were accompanied with still shorter

dark periods. A long-day plant, which normally flowers in a day length of 16

hours of a normal 24 hours cycle of light and darkness, can also flower if it gets 8

hours of light of a 12 hour cycle of light and darkness. Thus the inhibition of

flowering in a long-day plant under short day is not because the photoperiods are

short but because the dark periods are too long. The long day plants can

justifiably be called short night plants.

Some of the example of long day pants are henbane (*Hyoscyamus,) Pea (Pisum

sativum) peppermign (Mentha piperita), Meliltus alba, Barley (Hordeum vulgar),

Bentgrass (Agrostic sativa), Orchard grass (Dactylish glomerata), Canary grass (Phalaris

arundinacea), Oats (Avena wheat grass Lolium spp). Timothy (Phleum spp). Swiss chard

(Beta vulgaris), etc

Day Neutral Plants

There are a number of plants which can flower in all possible photoperiods ranging form

few hours to 24 hr of uninterrupted light exposure. They are also called photonerutrals or

indeterminate plant. The examples of such plants are Bluegrass (Poa annua), Corn (Zea

mays) Balsm (Impatiens balsamia), Bean (Phaseolus spp.). Buckwheat (Fagopyrum

tataricum), Cotton (Gossypium hirsutum), Cucumber (Cucumis sativus), Holly (Hex

aquifolium), Jerusalem artichoke (Helianthus tubersosus), Potato (Solanum tubersum),

Rhododendron (Rhododenadron spp.) Strawberry (Fragaria chiloensis), Tobacco

(Nicotiana tabaccum), Tomato (Lycopersicon esculentum).