PARTITIONING OF ASSIMILATES AND SOURCE SINK RELATIONSHIP

IN RICE

PHYSIOLOGY OF GROWTH,YIELD AND MODELLING

PRESENTED BY:-

K. AMAR PRASAD RAM/15-35

M.Sc (Ag) GPBR

Translocation

PHLOEMSOURCEe.g. palisade cell

SINKe.g. fruit

Translocation is the movement of organic solutes e.g. SUCROSE, from a source to a sink through the phloem by means of mass flow

The sucrose transporter gene in Rice is OsSUT1

Source, sink, and translocation capacity of assimilates play important roles during the formation of grain yield.

A study was conducted to characterize the genetic bases of traits representing source, sink and transport tissue, and their relationships with yield traits in rice, by analyzing QTLs for these traits and various ratios among them.

The results showed that close linkage or pleiotropy is the genetic basis for the correlations of grain yield traits with source, sink, transport tissue and the various ratios among them. and also suggest that improvement in ratios among source, sink and transport tissue may result in improvement in yield potential.

Genetic studies for quantitative traits have been greatly facilitated by the development of various molecular markers.

The use of quantitative trait locus (QTL) mapping has contributed to a better understanding of the genetic basis of many agronomically important traits such as grain yield.

In rice, many researches have identified QTLs for grain yield and its components

RESULTS OF STUDYIn rice, the upper leaves are the main source of

assimilates for grain filling. Large sink size is a prerequisite for high yield and high harvest index.

Areas of the topmost three leaves were not correlated with 1,000-grain weight, and were negatively correlated with grain-filling percentage and grain yield, respectively.

Total spikelets per panicle and the number of large vascular bundles were also negatively correlated with grain weight, grain-filling percentage and grain yield.

The ratios of areas of the topmost three leaves to spikelets per panicle were positively correlated with 1,000-grain weight.

The correlation between the ratio of LVB to flag leaf area was not significant.

However, the ratios of LVB to the areas of the –2nd and –3rd leaves were positively correlated with grain yield and grain-filling percentage, respectively.

Relationship between source-sink charactersand yield traits Correlations between leaf areas and yield traits were not always

strong, Both positive and negative correlations between grain yield and leaf-area index (LAI) have been reported, depending on LAI value.

A negative relationship between LAI at flowering and grain yield was often observed at a high LAI in rice.

However, it is inconsistent with the report of Li et al. that alleles increasing source leaf size were associated with increased grain yield.

From the viewpoint of crop physiology, firstly, it is often noted in a rice canopy that the –2nd and –3rd leaves are mutually shaded during grain filling. In this case, their net photosynthetic capacity is low and may become net consumers of assimilates.

Secondly, it is often observed that negative correlation occurs between leaf area and photosynthetic rate.

Such observations suggest that larger leaf area does not always provide more assimilates to the grain during grain filling.

Assimilate partitioning should be considered in designing the plant type for yield improvement.

The ratio of leaf area to spikelet number represents the available source per spikelet and could be a critical physiological parameter influencing grain weight.

The topmost three leaves are considered to be sources for yield formation.

Flag leaf area per spikelet was positively correlated with yield traits.

However, the –2nd and –3rd leaf area per spikelet was negatively correlated with grain yield and grain-filling percentage.

1- Transplanting stage

2- Critical stage for effective

tillering

3- Elongation stage

4- Booting stage

5- Heading stage

6- 5 days after heading

7- 15 days after heading

8- 25 days after heading

9- 35 days after heading

10- Maturity stage

LAI and stage of development

Booting stage-heading Maximum LAI

DMA from elongation to heading related with the accumulation during the grain filling stage and yield.

40%

GY

PARTITIONING IN VEGETATIVE STAGE

• Among the tillers, the pattern of panicle development is hierarchical and grain yield becomes poorer in each successive tiller. Usually panicles of the late-formed tillers on higher nodes do not contribute to grain yield .

• A high yielding semi dwarf rice plant produces a large number of tillers, one in each successive leaf axil at different time intervals; the initiation and development of the tillers are staggered and temporally spaced, but maturation is synchronous.

• Therefore, a late-formed tiller on a higher culm node senesces earlier than that of an older tiller and contributes less in grain number and yield.

• Although genetic potential does not restrict tiller development, pre- mature senescence of the newer tillers limits grain yield by reduction of effective panicle number of the plant and number of grains on the newer tillers.

• Grain number per panicle is a plastic yield component; the spatial location of the tiller determines panicle grain number.

• Conversely, the other components like effective tiller number and grain weight are under genetic control.

• Therefore, regulation of tiller dynamics is important for crop management; too few tillers limit grain yield and too many tillers result high tiller abortion, poor grain filling and reduction of panicle size.

• The manner, in which an ordered pattern of tiller senescence in basipetal succession impacts source capacity for grain filling and thereby determines grain yield in each tiller is not known.

• Similarly, the physiological advantages enjoyed by an older tiller over that of a relatively new tiller for grain filling and the bias against development of the latter are unclear. In this study, it was desired to compare the senescence pattern of the photo- synthetic tissues of the main shoot, primary and secondary tillers during the period of reproductive development.

POST-HEADING REMOBILIZATION OF STARCH

Leaf sheaths of higher position leaves (upper leaf sheaths) on rice (Oryza sativa L.) stems function as temporary starch storage organs at the pre-heading stage.

Starch is quickly accumulated in upper leaf sheaths before heading, but the storage starch is degraded at the postheading stage to provide the carbon source for developing grains.

Abscisic acid (ABA) is a key plant hormone to control plant development and stress responses.

This study found that ABA content in upper leaf sheaths was significantly increased at the stage after panicle exsertion and that the pattern of ABA increase was negatively correlated with changes in starch content.

Exogenous ABA reduced starch content in leaf sheaths while the activities of starch degradation enzymes (i.e., a-amylase) increased in ABA-treated leaf sheaths and sucrose transporter gene expression was up-regulated.

ABA plays an important role in promoting starch degradation and sucrose remobilization in upper leaf sheaths at the post-heading stage.

References :1. Molecular dissection of the genetic relationships of source,sink

and transport tissue with yield traits in rice K.H. Cui ・ S.B. Peng ・ Y.Z. Xing ・ S.B. Yu C.G. Xu ・ Q. Zhang2.Abscisic acid enhances starch degradation and sugar transport in rice upper leaf sheaths at the post-heading stage Huai-Ju Chen • Shu-Jen Wang