Agriculture Reference
In-Depth Information
Effect of B on Photosynthesis
Photosynthesis is a complex series of reactions that culminate in the reduction of
carbon dioxide. The effect of B nutrition on photosynthetic processes has been
rarely studied. Decreases in B supply reduce soluble proteins and chlorophyll in
leaves, which are important constituents for Hill reactions and photosynthesis
(Mukhopdhyaya et al.
2013
).
There was no direct involvement of B on rate of photosynthesis, but from recent
research it is evident that B has a positive effect on photosynthesis under normal
(optimum) level. Moreover, there are reports of increases in chlorophyll pigment
and carotenoids by foliar spraying of B leading to increases in photosynthetic rate
(Thurzo et al.
2010
). Ganie et al. (
2013
) also showed that net photosynthetic rate
was increased due to increases in plant light harvesting pigments such as chloro-
phyll and carotene in the leaves.
B deficiency negatively affects photosynthesis by decreasing photosynthetic
oxygen evolution rates and hence the efficiency of photosystem II (Kastori
et al.
1995
; El-Shintinawy
1999
). Photosynthetic rate (
P
n
) drastically decreased in
cotton plants when grown in B deficient soil (Zhao and Oosterhuis
2002
). It was
reported that inhibition of photosynthesis was a result of reduced Hill reactions and
low intercellular CO
2
concentrations (Sharma and Ramchandra
1990
). Some exper-
imental evidence indicated close relationships between gas exchange parameters
and B deficiency, implying that these parameters were possibly affected by external
B supply and in turn prejudiced growth. Previous studies, under B deficiency,
supported a change in photosynthetic enzyme activities that were undoubtedly
involved in a decrease in
P
n
(Sharma and Ramchandra
1990
). B deficiency was
followed by reduction in the leaf stomatal conductance (
g
s
) and rate of photosyn-
thesis (Huang et al.
2005
; Han et al.
2008
). Related declines in plant
g
s
at B
deficiency were initiated by high oxidative damage in leaves (Huang et al.
2005
).
Moreover, low
g
s
also decreases E (Han et al.
2008
). It was advocated that the
presence of free hexoses can elicit regulation of the Calvin cycle and, hence, can
obstruct
P
n
(Han et al.
2008
). A diminution in pigments under B deficiency was
shown for citrus (Han et al.
2008
). The synthesis of unnecessary starch possibly
disrupts chloroplast structure, leading to poorer CO
2
assimilation and decreased
chlorophyll content (Han et al.
2008
). It is likely that B deficiency caused changes
in chloroplast structure, which eventually affected pigment content (Pandey and
Pandey
2008
). B deficiency may also affect photosynthetic responses by the
modifications in the structure and function of chloroplast thylakoids.
Effect on Reproductive Growth
According to Loomis and Durst (
1992
) B is essential for generative growth. Boron
is involved in metabolism of carbohydrates and phenolic acids, which are crucial
