Agriculture Reference
In-Depth Information
Many self fertilizing crops are particularly sensitive to
abiotic stress at the reproductive stage. In rice and wheat, for
example, abiotic stress during meiosis and young microspore
stage indicates the developmental program appears to be
compromised. Tapetal hypertrophy can occur as a consequence
of cold and drought stress, and programmed cell death (PCD)
is delayed or inhibited. Since the correct timing of tapetal
PCD is essential for pollen reproduction, substantial losses in
grain yield occur. In wheat and rice, a decrease in tapetal cell
wall invertase levels is correlated with pollen abortion and
results in the amount of hexose sugars reaching the tapetum,
and subsequently the developing microspores, being severely
reduced. ABA and gibberellins levels may be modifi ed by cold
and drought, infl uencing levels of cell wall invertase(s) and
the tapetal developmental program, respectively. Many genes
regulating tapetal and microspore development have been
identifi ed in Arabidopsis thaliana (L.). Heynh and rice and the
specifi c effects of abiotic stresses on program and pathways
can now begin to be assessed (Parish et al. 2012).
Chilling during male gametophyte development in rice
inhibits development of microspores, causing male sterility.
Changes in cellular ultrastructure that have been exposed
to mid chilling include microspores with poor pollen wall
formation, abnormal vacuolation and hypertrophy of the
tapetum and unusual starch accumulation in the plastids of
the endothecium in the post meiotic anthers. Anthers observed
during tetrad release also have callose(1,3-β-glucan) wall
abnormalities (Fig. 24).
Expression of rice anther specific monorepressed
genes(OsMST8) is greatly affected by chilling treatment.
Perturbed carbohydrate metabolism, which is particularly
triggered by repressed genes OsINV4 and OsMST8 during
chilling, causes unusual starch storage in the endothecium and
