Exposure of 28-day-old rice seedlings for 6 days to 150 mm NaCl was found to induce drastic decreases in relative water contents, chlorophyll, and proteins in the leaves. This effect was largely prevened when before the exposure to NaCl the seedlings were treated for 4 days with 15 mm glycinebetaine. Although rice plants do not accumulate glycinebetaine endogenously, added glycinebetaine was found to be taken up by the roots and to accumulate in the leaves to reach a concentration of up to 5.0 μmol per gram fresh weight. The level is comparable with those of barley and wheat, which are well known glycinebetaine accumulators, under salt stress. The quantum yield of PSII was decreased by 27% under salt stress. This decrease was also largely prevented by glycinebetaine application.

To study the characteristic features of the amyloplast, a uniquely differentiated plastid-type which synthesizes and accumulates reserve starch, in comparison with those of the chloroplast, these two types of plastids were isolated from white-wild and green-mutant protoplasts of cultured sycamore (Acer pseudoplatanus L.) cells, respectively. The intactness of the isolated amyloplast preparations was 70%. Electron microscopic ultrastructural analysis of both plastid types revealed unique structural features of the green-mutant chloroplasts, including well developed grana membranes and abundant ribosomal particles and plastoglobuli. After osmotic rupture of the isolated amyloplasts and chloroplasts, a clear separation of the envelope-membranes was achieved by discontinuous sucrose density gradient centrifugation. Although the visible absorption spectra of the envelope lipid components were indistinguishable between the amyloplasts and chloroplasts, the envelope-membrane polypeptide patterns were clearly distinct as judged by denaturing electrophoresis. By immunoblotting analysis using the specific antiserum raised against the pea chloroplast 29-kilodalton Pi-translocator, the amount of this carrier-protein (31-kilodalton) in the white-wild amyloplast envelope-membranes was estimated to be at least 10-fold less than in the green-mutant envelopes.The amyloplast is a uniquely differentiated plastid-type which synthesizes and accumulates starch in the stromal matrix. It has long been hypothesized that this organelle is ontogenically and I

To investigate the antioxidant defense system, salt-stress induced changes of antioxidant enzymes were examined in the leaves of mulberry (Morus sp.) of the salt-tolerance cultivar Pei. With increasing salinity up to 150 mM NaCl, the hydrogen peroxide content and the activity of guaiacol-specific peroxidase increased markedly. In addition, the activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase slightly increased at 150 mM NaCl. In contrast, catalase activity with increasing salinity was not correlated with hydrogen peroxide content. The results suggest that under increasing salinity, the primarily prominent peroxidase activity appears to play an active role in scavenging reactive oxygen species in this cultivar, whereas the superoxide dismutase/ ascorbate-glutathione cycle seem to be important consequently.

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Amyloplast envelope membranes isolated from cultured, white-wild cells of sycamore (Acer pseudoplatanus L.) have been found to contain a Mg2 -ATPase, ranging in specific activity from 5 to 30 nanomoles per minute per milligram protein. This ATPase hydrolyzes a broad range of nucleoside triphosphates, whereas it hydrolyzes nucleoside mono-and diphosphates poorly, if at all. The ATPase activity was stimulated by several divalent cations, including Mg2 , Mn2 and Ca2+, whereas it was not affected by Sr2 , K+, or Na . The Km for total ATP was 0.6 millimolar, and the activity showed a broad pH optimum between 7.5 and 8.0. The ATPase was insensitive to N,N'-dicyclohexylcarbodiimide and oligomycin, but it was inhibited by vanadate. All these characteristics are basically similar to those reported previously for the Mg2+-ATPase of the chloroplast inner-envelope membrane. Likewise, the amyloplast envelope enzyme was shown to be located specifically on the inner envelope membrane. The amyloplast envelope membranes were chemically modifled with a series of unique affinity labeling reagents, the adenosine polyphosphopyridoxals (M Tagaya, T Fukui 1986 Biochemistry 25: 2958-2964. About 90% of the ATPase activity was lost when the envelope membranes were preincubated with 0.1 millimolar adenosine triphosphopyridoxal. Notably, the enzyme was protected completely from inactivation in the presence of its substrate, ATP. In contrast, both adenosine diphosphopyridoxal and pyridoxal phosphate caused much less of an inhibitory effect. This greater relative reactivity of the triphosphopyridoxal analog is similar to that reported previously with Escherichia coli F1 ATPase (T Noumi et al. 1987 J Biol Chem 262: 7686-7692).The occurrence of a DCCD3-insensitive Mg2+-ATPase has been reported in the chloroplast envelope membranes from spinach (3,11,15,22,23), pea (5, 16-18, 21, 28) (8) reported the presence of a DCCDinsensitive Mg2+-ATPase apparently associated with the amyloplast envelope from etiolated epicotyls of Pisum sativum, the putative ATPase of the amyloplast envelope has not been well characterized. The aim of our study was to characterize the ATPase ofthe amyloplast envelope for the further understanding of its possible function(s) in this unique plastid-type. In addition, we have established a method for resolving the inner and outer membranes of the amyloplast envelope in order to determine the location ofthe ATPase, and we have found that it is localized on the inner membrane, similar to that in green-leafchloroplasts (3,17,18,21).Fukui, Tagaya, and coworkers (24,30,31) previously synthesized nucleoside polyphosphopyridoxal compounds and tested their potential affinity for several ATP-binding enzymes such as adenylate kinase and lactate dehydrogenase. The analysis of the modified enzymes indicated that these afflnity labels were exclusively bound to the active site lysyl residue of the enzyme with much higher specificity than that of pyridoxal phosphate. In this study, we also examined and compared PLP, AP2-PL, and AP...

Multiple shoots of mulberry (Morus alba cv Khonpai), a NaCl-tolerant cultivar, were grown on MS media without or with NaCl. On medium with increasing NaCl concentration up to 150 mM, the shoots exhibited slightly reduction in growth. On the other hand, when the concentration of NaCl increased to 200 mM, the growth was completely inhibited and the necrosis of leaves tissue was observed. The relative water content was significantly decreased in leaves treated with NaCl concentration of 150 and 200 mM compared to that in leaves without NaCl treatment. The total chlorophyll content was significantly lower in leaves of salt treated multiple shoots than in leaves of control multiple shoots. Comparing shoots grown on media without to with 150 mM NaCl, the proline content in leaves was increased to approximately 11-fold and the ascorbate peroxidase activity in leaves was increased to approximately 91%.

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