Indian J. Plant Physiol .• Vol. XXVII, No.3 pp. 232-238 (September 19a4)
STUDIES ON ASSIMILATE TRANSLOCATION IN RELATION TO YIELD IN GROUNDNUT
U.K. SENGUPTA AND ARUNA SHARMA
Division of Plant Physiology, Indian Agricultural Research Institute. New Delhi·IIOOll
SUMMARY
Labelled uCOa was fed to the leaves of different branches during pod development and translocation of assimilated I,C was measured from different plant parts of ground nut (Arachis hypogea L.) cultivars. It was observed tbat cv. J-ll incorporated bigher amount of I4CO. but tbe assimilate translocation to other plant parts was lesser compared to cv. M·13. DUring peak pod developmental stage most of tbe translocated HC was recovered from the pods of M·13. wbile a small amount from the pods of J·l1.. I.t was suggested tbat tbe bold seed and bigh yield in M·13 may be due to better sink efficiency and partitioning of photosyntbates as compared to J·11.
INTRODUCTION
Groundnut crop (Arachis hypogea L.) is characterised by indeterminate growth habit in that its terminal meristem never becomes reproductive and there is no precise end to vegetative growth. Ingroundnut crop fast vegetative growth starts only after flowering and it continues till maturity (Williams et al., .1975). The LAl of some cultivars continues to increase more than 7.0, sugges
ting that there is considerable yield potential present in terms of photosynthetic accumulation (Duncan, 1978). Low yield of the crop may be due to numerous factors besides external factors. such as, inhibited photosynthesis, inadequate distribution or insufficient metabolic supply or all may be involved. It has been shown that though ground nut plant operates C·3 pathway, it has high photosynthetic rate (50 mg COli dm-2hr-1) which is comparable to efficient
.~
....
"ASSIMILATE TRANSLOCATION GROUND NUT 233
MATERALS AND METHODS
Groundnut cuItivars respresenting high yielding bold seeded M-B and a low yielding small seeded J-ll were raised in the field of TART. New Delhi. The crop was sown during the growing season favourable for the optimum growth with one irrigation at planting and as needed during the growing season. Labelled 14COz was fed to the leaves at two stages of pod develop ment : (i) 30 days after flowering i.e. initial stage and (ii) 80 days after flowering respresenting peak stages of reproductive growth and development. 14COz was fed to the leaves of four branches vide. first. third. fifth from the basal node and the main shoot. The top fully expanded leaf of each branch was exposed to 14COz insi de a plexi glass chamber for 30 minutes and the whole plant including the uC02 fed leaves were harvested 48 hours after
feeding. The distribution pattern of assimilates was expressed on the basis of total incorporation of
Uc
by the whole plant (Sharma et al. 1981).RESULTS
The translocation of assimilates from the main shoots did not show apparent varietal difference during the initial stage of pod development (Table
O.
However, the distribution of translocated assimilates was better in J -11 as the branches other than 14C02 fed branch and pods accumulated more HC as compared to M-13. Translocation to the pods and pegs from the main shoot was 11%
in J-11 and 2% in M -13. It was observed that most of the incor porated l4C was retained in the fed leaves of both the cultivars. Translocation of assimilates from the leaves of branch-I was comparatively better in M- 13 . (14%) and its distribution was found to be uniform to other plant partsincluding pod and roots. In J-ll the translocated l'C moved mainly to the pods and roots. Both the cultivars showed higher amount of assimilate translocation from the branch-3 as compared to other branches during initial stage. But the distribution pattern of translocated 14C from branch-3 showed that about 82% in J-ll and 49% in M-13 did not move out of the rest of the 14C fed branch. The distribution pattern from this branch was better in M-13 as it translocated more 14C to the roots and other branches. Tn branch-5 most of the 14C were recovered from the vegetative parts. During this initial stage of pod development supply of assimilates to the pods and roots was more from the main shoot and branch- J, while the assimilates from branch-3 and 5 were supplied to the vegetative parts.
Table 1: Pattern of translocation of photosynthates from branches to various plant parts during initial stage of pod development ~
'"
1-11 M-13Main Shoot
Branch-I
Branch-3
Branch-5
Main Shoot
Branch-I Branch-3 Branch-S Total uC in plant (dpm) 65320 56660 41920 5580 90290 21570 27530 11320 14C Retained in red leaves (dpm) 58720 51040 29700 4640 80600 18490 21760 9090
c:
Per cent I,C retained in red leaves I,C Translocated (dpm) Per centuc
translocated Per cent distribution or translocated HC in plant parts: Rest or the red branch Othor branches Pegs and pods 89 •• 96600 10.10 16.82 53.18 11.06 90.08 5620 9.92 41.46 15.84 19.57 70.85 12220 29.15 82.73 6.55 5.15 83.85 940 16.85 49.08 28.70 10.02 89.27 9690 10.73 24.87 49.12 2.58 85.72 3080 14.28 28.25 29.54 25.97 79.04 5770 20.96 49.05 24.96 ••
66
80.30 2230 19.70 47.15 30.88 9.41
~ rn l'I:I
S
c:
~ > > Z ~ >i
> rn >=
;
>Table 2 : Pattern of translocation of photosynthates from branches to various plant parts during peak stage of pod development 1-11 M-13 Main Main-13 Shoot Branch·l Branch-3 Branch-5 Shoot Branch-I Brancb.3 Branch-5 Total uC in Plant (dpm) uC Retained in fed leaves (dpm)
109010 103730 78490 75290 194430 178800 19910 16660 117500 89750 34930 26120 11"20 112010 27310 24100
>{I.I \'n
...
lC-Per cent uC retained in fed leaves 95.16 95.92 91.96 83.68 76.31 74.79 93.72 88.24
I'" > 00'\1 t!I
uC Trallliocated (dpm) 5280 3200 1'630 32'0 27750 8810 7510 3210
00'\1 \III >
Per cent uC translocated 4.84 4.08 8.04 16.32 23.62 25.22 6.28 11.75 ~
~
Per cent distribution of translocated 14C in plant parts:i
Rest of the fed Branch 30.30 20.63 67.82 40.01 19.47 16.57 lUI 23.05Q ~
Other
branches
Pep
and
pods
25.76 19.32 20.62 20.31
1.'7
13.82
39.38 15.38
11.4' 63.56
8.28 '0.18 2',6' 31.04
52.01 12.17 c: Z 1:1 Z c: 00'\1
Iloots 24.62 38.44
'.71
"23 5.48 24.97 24.36 12.77"-> 1M VI
236 U.K. SENGUPTA AND ARUNA SHARMA
At this stage also a large percentage of 14C still remained in the fed leaves in all the branches. In J-11 the percentage of translocated 14.C from the fed leaves decreased as compared to the initial stage from all the branches while it increased from main shoot and branch-l of M-l3. In the main shoot of J-ll the 14C fed leaves retained about 95% of the assimilated HCOl! as against 76% in M-l3. The distribution of translocated 14C from the main shoot was also better in M-l3 as 63% recovered from the pods as compared to 19% in J-I1. The supply of assimilates to the roots was better in J-l1 than in M-13. Similar to main shoot. translocation from branch-l was more in M-13 (25%) as com pared to J-Il (4%). About 50% of the translocated 14C from the branch-l of M-13 was exported to the pods and it was only 20% in J-11. The translo located 14C from the leaves of branch-l was distributed uniformly to all other plant parts in J-l1 but it was exported mainly to the pods in M-l3. Both the cultivars showed a poor translocation from the branch-3. Most of the translocated 14C from this branch moved to the rest of the fed branch in J-11 while pods were the main sink in M-13. The fifth branch. which was comparatively less developed showed higher assimilate translocation than branch-3 in both the cultivars. But most of the translocated l4C was recovered from the rest of the fed branch and other vegetative parts. Pegs and pods received a small amount of assimilates from this branch.
DISCUSSION
The results showed that the top young leaves which were fed with labelled HCOlj, retained the major amount of HC in the fed leaves itself and only a small part of it was exported to other plant parts. This was observed irrespective of variety and the position of branches on the main stem. Even during peak pod developmental stage. percentage translocation out of the HCOl! fed leaves was rather poor. This may be due to inderter minate and continuos growth of the crop and the assimilates might be utilised for its own vegetative growth (Sharma et al.• 1981).
Varietal difference regardi ng partitioning ability was observed during both initial and peak stages of pod development. At initial stage. the main shoot of J-l1 supplied the translocates to other branches. roots and pods. But the cuItivar M-l3, although retained the same amount of lebel in the 14(;0 l! fed leaves as in J-Il. did not translocate to the pods but supplied to the vegetative parts only. This would indicate that the main shoot of J-11 had efficient partitioning than M-13 at this stage. But the translocation f~om
ASSIMILATE TRANSLOCATION GROUNDNUT 237
recovered from the 14C02 fed branch and partly translocated to the roots. The different type of partitioning observed in these two cultivars may be due to development of maximum number of pods in branch-l of M-13 and at the base of main shoot in J-l L Although the translocation of assimilates from branch-3 and 5 was better in M-13, it appears that most of the assimilates from these two branches were used for its own vegetative growth and partly used for pods. In both the cultivars, roots received a good percentage of label from all the branches.
During the peak pod developmental stage assimilate translocation to the pods increased in M-13 but decreased in J-11 as most of the assimilates were retained by the fed leaves. This may be due to 3-4 days early flowering
in J-ll and therefore at second stage, it may not be same active stage of pod
238 U.K. SENGUPTA AND ARUNA SHARMA
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