source sink relationship in rice

1. 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

3. Translocation
PHLOEMSOURCE
e.g. palisade cell
SINK
e.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

4.  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.

5.  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

6. RESULTS OF STUDY
In 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.

7. 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.

8. Relationship between source-sink characters
and 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.

9. 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.

10. 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.

11. 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

12. DMA from elongation to heading
related with the accumulation
during the grain filling stage and
yield.
40%
GY

13. 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.

14. • 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.

15. • 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.

16. • 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.

17. 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.

18.  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.

20. 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. Zhang
2.Abscisic acid enhances starch degradation and sugar transport
in rice upper leaf sheaths at the post-heading stage
Huai-Ju Chen • Shu-Jen Wang