CHLOROPHYLL AS AN INDICATOR OF LIGHT INTENSITY IN ANDROGRAPHIS PANICULATA

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f,dian.!. Plant Pltysiol., Vol. 4, No. I, (N.S.) pp. 15- I 'J (Jan.-March, 1999)

CHLOROPHYLL AS AN INDICATOR OF LIGHT INTENSITY IN

ANDROGRAPHIS PANICULATA

PRATIMAKAPUR

Department oC Botany, Mahila Mahavidyalaya, Banaras Hindu University Varanasi- 221005

Received on 2 Jan, 1998, Revised on 10 Nov., 1998

SUMMARY

Impact 'f light intesity on Andrographis paniculata showed that increasing light reduces the chlorophyll content on unit leaf area, land area as well as per gram dry weight basis. Light and age had significant effect on the chlorophyll content. Both, chlorophyll a and b were significantly affected by light. A negative correlation was observed between light and chlorophyll alb ratio.

Key words: Andrographis, chlorophyll, light intensity.

INTRODUCTION

Light, \\hich predominantly originates as a radiant flux, is unique among the environmental factors as a driving variable and individual organisms may be affected by any one of its aspects of intensity, colour, duration and direction. Among these, intensity of light nevertheless is most critical variable influencing photosynthesis through its absorption by chlorophyll (Treshow, 1970).

As a characteristic of the family Acanthaceac, leaves of Andrographis paniculata also change colour from green to red and vice versa from time to time. The reddening begins with the onset of the flowering and is delayed by a vYeek in shaded plants. Keeping this in view, the experiments were conducted to understand the behaviour of the chlorophyll under different light conditions. A slight fluctuation in the chlorophyll is enough to trigger changes in physiological processes of the plants including photosynthesis. Thus, in dry matter production, chlorophyll plays one of the most basic role.

MATERIALS AND METHODS

given four light intensity treatment. One set of plants was kept in the open, without attenuating light and was considered as plants under 100% relative light intensity (RLI), while the other three sets were kept under 15. 30 and 45% of the total light by attenuating light by thatching. Chlorophyll content of leaves, stem and inflorescence was detennined in plants of different age following Amon ( 1949), and further estimation on unit dry weight basis was done according to Wood and Bachelord (1969) Quantitative estimations were done for chlorophyll on unit leaf area basis, per unit land area as well as its distribution pattern. Chlorophyll index ( C I) was calculated according to Singh ( 1974).

CI = Total chlorophyll Ground area

RESULTS AND DISCUSSION

The detrimental effect of light intensity on the chlorophll content per unit leaf area (mg em-=) is evident from Fig. lA, and a negative correlation (r = -0.94) was also observed between the two With age, a rise was Andrographis paniculata (Burm. F.) Wall ex Nees., recorded up to 93 days in each of the four light regimes, a member of family Acantahaceae and a bitter shrub was followed by a fall up to 212 days. beyond ,,hich the trend

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is not very clear. A negative correlation was obtained Table I

between chlorophyll (mg cm-2

) and NAR (r = -0.91) and

Variation in the chlorophyll a/b ratio of Andrographis panicu!ata with light and age.

SLW (r = -0.83).

Similar to chlorophyll per unit leaf area, the chlorophyll per unit dry weight (mg g·1

) also bore a

negative correlation (r = -0. 99) \\ith light. The value in this case too increased up to 93 days. where the first peak was recorded at all the light levels. A decline however. followed differently under different light condition. A second peak was recorded at 273 days in 15,30 and 100% RLI plants, while it was attained a month earlier at 243 days in the 45% exposure plants (Fig. 1 B). the values then declined and rose sharply again under shaded condition to yic:ld a third peak at 333 days coinciding with the peak of the second \Cgetative stage. The highest value of 19.68 mg g·1

\\as recorded by the 15'1';, RLI plants at 93 days.

Chlorophyll content (mg m2

) was signifncantly

;.lffected both by light as well as age of the plants. With ltght, chlorophyll followed a decreasing trend at almost all the ages and a significant relationship (r = -0. 90) was obtained between the tvvo. \Vith age. an increasing trend was obtained up to 123 days in the upper three light regimes \\bile at the 15% level it continued to increase up to 153 days. After a brief slack period, the values started rising again at 183 days in the 30 and 45°/r, and at the 243 and 7""'3 days in 15 and I 00% plants respectively. (Fig 1 C). The peak \vas obtained at 3 3 3 days, in each of the four light intensities.

Significant variation in the chlorophyll content was brought forth by its components a and b. Chlorophyll a/ b ratio showed a significant negative correlation (r =

-0. 95) with light. With age, the ratio declined up to 212 cl:1ys and then increased steadily (Table l)

Relative distribution of chlorophyll(% of total) in the component parts presented in Fig. 2. does not reveal any consistent trend with light. With advancing age, leaf showed a decline up to the second flowering stage. but reco\ ered thereupon (Fig. 2). Contrary to the leaves, stem showed an increasing trend of chlorophyll up to 153 days

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RelatiYe light intem;it\ ('% 1

Age (days) !()() 45 30 15

52 245 2.5lJ 24R 2.69

71 2.33 2.32 240 2.49

93 1.55 141 2.71 2.G3

123 1.41 I ' ' ... ,'!,) 261 240

!53 1.48 I.R'! 2.51 2.67

1R3 133 2.W> 1.')7 2.2R

212 115 07') l 90 1.7')

243 JR7 2()3 1.94 1.90

273 l.R7 2.2c.l 240 2.11

303 1.70 2.73 2.86 2.77

333 2.91 2.R2 2.97 2.87

2(13 3.16 .un 2.95 3.1 ~

0·0'

-"

A

~ 0·04 I ~,....·,. \ ...

__ ... -··;.~---

.•

~-···· .. ..._.r ., .'

I

.,

· . . --~---. _I _'.-·-· ilr'"":..:_-:_· I ""'"\

~

-.... :1 --1 E" _0·01 -"-<\~-·-·-i/

\.J

60 _t...₆_{<L:o--::C:,2o:---,-:-,oo=--~240::---="""=----~,.:-::-'o}

6 (, E: f 0 .. " . l •

Fig. I : Chlorphhyll content A · mg em' lear area, B . mg g-1 _dry

\\eight, C : mg m·'land area in tour light regimes during gnmth period of A. paniculata.

in the p !ants exposed to 3 0'% RLI and up to 183 days in 15 and 100'/'o RLI plants while up to 212 days in 45% RLI plants. A decline after this persisted up to the end, except at 363 days where the values rose again with the luxuriant grovvth of rejuvenated plants. In case of inflorescence, an

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CHLOROPHYLL AND LIGHT INTENSITY

RLI- 15% 30% 45% 100%

~8~y~f ~

I

~ ~ ~

I

71 ~

J

g

_E3 §

Egj

I

100°/o CHLOROPHYLL DISTRIBUTION PATTERN ("to OF TOTAL)

Fig. 2: Distribution of chlorophyll ('Yo of total) in photos\nthetic parts /1. paniculata under four l;ght kvcls

increasing trend was observed only up to I X3 days in the

mitial three intensities, after which the values dropped. Tn I 00%) RLT plants, the increase was seen up to !53 days

followed by a sharp fall and values picked up again from 183 days except for a sharp fall at 273 days (Fig. 2)

An inverse relation of CI \Vith light intensity \\as

observed at almost all the ages (Table II) a linear increase

''as obsen ed \\ith advancing age up to 93 days in all the

light regimes. The values remained steady up to 123 days

in the initial intensities and up to 183 days under full

exposure, followed by a fall and rise differently under

different light intensities. Mostly the values rose at lo\\er

lights The peak of CI \\as obtained at different ages by the different light plants.

Chlorophyll is the most imp011ant basis of dry matter

production on the earth. A h1gh level of dry matter

production is possible when chlorophyll is present in a significantly high amnunt. Reddening of leaves \\ith

increasing light coupled With a decline in total chlorophyll is evident from the negative correlation obtained bet\\een

chlorophyll and light intensity. Anthocyanian synthesis.

lnd1tmJ P/,1/il Phy.,1ol .. VoL 4. :\o.l. (1\.S.) pp. 15-19 (Jan.-1\larch. 199'))

which imparts colour to the leaves under full exposure ts

promoted by high light intensities moderatly lo\\

temperature and adequate supply of sugars (Salisbury

and Ross 1974 ). The lowering of temperature under

shaded condition, coupled \\ith a reduction in the

assimilation rate, hampering the supply may be a contributory to the reduced reddening of leaves and

consequently delayed senescence of the plants under lo\\ light intensities. Higher light intensities have a damaging

effect on the chlorophyll, both on weight as well as area

basis. This is substantiated by a sequential reduct10n in

chlorophyll content as the intensity of light increased, which was also reported by Naidu and Swamy ( 1993) and

Laing et ol. _ ( 1995). Pemmal and Rao ( 1991) also obsend

that a real reduction to 30% light, increases the chlorophyll

content in cotton plants. Decrease in the chloroph: II

content of the plants may be related to the fact that the

leaves mature rapidly as \veil as age and fall earlier under sunny conditions. Higher concentration of chloroph) II in

the herb layer under trees and shrubs were also shown by

Ovington and Lav\fence (196 7). who reported that the average chlorophyll content of the living material of the

Table II Effect of light and age on chlorophyll index

(CI-mg cm-2₎

Relative lig_ht mtcnsitv ('Yr,)

Age (days) ]0() 45 311 15

52 0 006 0.006 0.0!3 () 014

71 () 014 0 017 ().(140 0 112X

93 ()()] 5 () ln'J () 1142 II (17}\ 123 () 015 0.0:\'J (I 042 11.117S

153 () 015 01125 OIUX () IIX5

IX3 I)()] :5 0 02:' 11.1140 0 115(,

212 0 Ill X 0 0 IX () 032 () 1159

243 0 ()]9 0 031 11113X () 1142

273 lUI I(, I) 025 11.053 () 125

303 (). 034 0 040 0.1155 1).(194

333 0. 10 I 0 1 c,x 0.234 II 1 XX

263 II()(,(, 0 072 ll21S 020X

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herb layer in the open prairie was always lower than that under Oak canopies.

Light affects not only the total chlorophyll but also its

~onents as is evident from a negative correlation

between light and chlorophyll alb ratio, which was also observed by Argyroudi-Akoyunoglou and Akoyunoglou (1970) in young bean plants. This was also observed by Clayton (1966) when the hours of exposure were raised which he has attributed to the fom1ation of the chlorophyll containing only photosystem I. In addition to this the light and dark cycle seems to be an ideal for testing that chlorophyll is a precursor to chlorophyll b (Akoyunoglou

eta!., 1967) and for examining further, the possiblity that the conversion of chlorophyll a and b is photochemical rather than biochemical. This however needs further

investigation in A. paniculata. Contrary to this

Masarovicova and Eilas (1981) and Naidu and Swamy (1993) observed that shading decreases a/b ratio. Detrimental effect of light on the chlorophyll per unit leaf area is evident from the negative correlation between the two in A. paniculata. Contrary to this Kirita and Hozumu ( 1973) presented a hyperbolic curve between chlorophyll per unit leaf area and mean relative illumination, while a linear relationship was obtained by Okubo eta!., (1975 b). Sharma and Sen (1971) also observed maximum chlorophyll per unit leaf area in Solanum nigrum Linn. when grown under continuous illumination. Cooper and Qua lis (1969) observed that shading increases chlorophyll on unit dry weight basis but decreases on unit area basis. Negative association of SLW with chlorophyll per unit leaf area shows that light favours the accumulation of photosynthates, while it reduces the assimilatory unit. In

contrast to this Okubo eta!. (1975a) obtained a significant positive correlation between chlorophyll mg cm-2 _and SL W. The relationship in the present investigation indicates that even though the light intensity inside the leaf must be reduced by the chloroplast pigments and even though the spectnun is alsC' changed in the direction of the wavelength of decreasing effectiveness, light was not enough to saturate chlorophyll accumulation at the sites available because under conditions in which leaf

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thickness increased, the site of chlorophyll formation decreased (Friend 1961). The negative correlation between chlorophyll per unit leaf area and NAR of Androgmphis paniculata may be due to the fact that the leaves with high chlorophyll content do not photosynthesize more rapidly because they probably lack the enzymes or coenzymes which are the product of light reaction for reducing the available C0

2 (Salisbury and Ross 1974) Reverse results vvere obtained on the other hand by Okubo et of.. ( 1975 a, b)

ACKNOWLEDGEMENT

The author is greatly indebted to Dr. K. C. Misra, Rtd. Reader of Botany, Banaras Hindu University, Varanasi, for guidance throughout the study period. Financial assistance from Post-Graduate Institute of Medical Sciences is gratefully acknowledged.

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CHLOROPHYLL AND LIGHT INTENSITY

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