We investigated responses of chloroplasts from flag leaves of a newly-developed super-high-yield rice (Oryza sativa L.) hybrid LiangYouPeiJiu (LYPJ) to water stress (withholding irrigation) during the grain-filling period. In the early stage of water stress (0-6 d) only the activity of Hill reaction was inhibited, whereas activities of photophosphorylation and Ca2+-ATPase, and ATP content were increased and peaked in the day 6 of withholding irrigation. In the late stage of water stress (6-12 d), the activities of photosynthetic O2 evolution, Hill reaction, photophosphorylation, and Ca2+- ATPase, and ATP content were significantly reduced. The membrane lipid content was sharply decreased, especially of sulfoquinovosyl-diacylglycerol (SQDG) and phosphatidylglycerol (PG). The changes in the ultrastructure of chloroplasts included mainly a decrease in number of grana and increase in number of osmiophilic granules. and G.-X. Chen ... [et al.].
The contraction of gastrointestinal (GI) smooth muscles is
regulated by both Ca2+-dependent and Ca2+ sensitization
mechanisms. Proline-rich tyrosine kinase 2 (Pyk2) is involved in
the depolarization-induced contraction of vascular smooth muscle
via a Ca2+ sensitization pathway. However, the role of Pyk2
in GI smooth muscle contraction is unclear. The spontaneous
contraction of colonic smooth muscle was measured by using
isometric force transducers. Protein and phosphorylation levels
were determined by using western blotting. Pyk2 protein was
expressed in colonic tissue, and spontaneous colonic contractions
were inhibited by PF-431396, a Pyk2 inhibitor, in the presence of
tetrodotoxin (TTX). In cultured colonic smooth muscle cells
(CSMCs), PF-431396 decreased the levels of myosin light chain
(MLC20) phosphorylated at Ser19 and ROCK2 protein expression,
but myosin light chain kinase (MLCK) expression was not altered.
However, Y-27632, a Rho kinase inhibitor, increased
phosphorylation of Pyk2 at Tyr402 and concomitantly decreased
ROCK2 levels; the expression of MLCK in CSMCs did not change.
The expression of P(Tyr402)-Pyk2 and ROCK2 was increased
when CSMCs were treated with Ach. Pyk2 is involved in the
process of colonic smooth muscle contraction through the
RhoA/ROCK pathway. These pathways may provide very
important targets for investigating GI motility disorders.