Photosynthetic control of plasma membrane H ATPase activity has been reported in vascular plants . Light induced cell expansion in Pisum sativum leaves partly depends on a DCMU sensitive stimulation of the plasma membrane H ATPase . In Vallisneria gigantia leaves, photosynthesis dependent modulation of the enzymatic activity of the plasma membrane H ATPase has been shown to be involved in lightinduced membrane hyperpolarization, which may have an effect on cytoplasmic streaming . However, there is no report of photosynthetic control of H ATPase phosphorylation. Thus, to our knowledge, the experimental evidence presented here is the first to show photosynthetic control of the phosphorylation status of the penultimate Thr of H ATPase in plants. Given that Suc also induced phosphorylation of the pT H ATPase in thalli , it is possible that light induced and photosynthesis dependent phosphorylation of the H ATPase is mediated by Suc as a photosynthetic product. Light induced phosphorylation, however, began within 5 min .
Further investigation will be needed to clarify the Seliciclib structure kinase inhibitor relationship between the time courses of Suc production and H ATPase phosphorylation in thalli. In vascular plants, the H ATPase plays a crucial role in the transport of photosynthetic products into sink tissues, such as fruits, tubers, and roots . In the case of phloem loading, Suc produced by photosynthesis in mesophyll cells is uploaded into the phloem companion cells by the Suc H symporter utilizing the electrochemical gradient generated by H ATPase and is transported to sink tissues via the phloem . However, the liverwort M. polymorpha is a nonvascular plant and has no phloem companion cells. Supplemental Figure S4 presents a cross section of the thallus, showing distinct layers of tissues: upper epidermis, photosynthetic parenchyma , storage parenchyma, lower epidermis, and rhizoids. The chlorenchyma is found just below the upper epidermis. Upper and lower epidermis may also contain chloroplasts. Storage parenchyma occupies the majority of the thallus.
Further investigation will be needed to elucidate the localization of the H ATPase in the thalli, which is phosphorylated Neohesperidin in response to light. This will clarify whether H ATPase phosphorylation is mediated by an intracellular or an intercellular signaling pathway and will elucidate the physiological role of the photosynthetic control of H ATPase phosphorylation in thalli. To understand how PKS5 regulates the PM H ATPase, we identified PKS5 interacting proteins using yeast two hybrid assays. To do this, we cloned the PKS5 cDNA into the pAS2 vector and transformed the resulting plasmid into yeast strain Y190. PKS5 was then used as bait to screen an Arabidopsis cDNA library .