SummaryAtHKT1 is a sodium (Na þ ) transporter that functions in mediating tolerance to salt stress. To investigate the membrane targeting of AtHKT1 and its expression at the translational level, antibodies were generated against peptides corresponding to the first pore of AtHKT1. Immunoelectron microscopy studies using anti-AtHKT1 antibodies demonstrate that AtHKT1 is targeted to the plasma membrane in xylem parenchyma cells in leaves. AtHKT1 expression in xylem parenchyma cells was also confirmed by AtHKT1 promoter-GUS reporter gene analyses. Interestingly, AtHKT1 disruption alleles caused large increases in the Na þ content of the xylem sap and conversely reduced the Na þ content of the phloem sap. The athkt1 mutant alleles had a smaller and inverse influence on the potassium (K þ ) content compared with the Na þ content of the xylem, suggesting that K þ transport may be indirectly affected. The expression of AtHKT1 was modulated not only by the concentrations of Na þ and K þ but also by the osmolality of non-ionic compounds. These findings show that AtHKT1 selectively unloads sodium directly from xylem vessels to xylem parenchyma cells. AtHKT1 mediates osmolality balance between xylem vessels and xylem parenchyma cells under saline conditions. Thus AtHKT1 reduces the sodium content in xylem vessels and leaves, thereby playing a central role in protecting plant leaves from salinity stress.

Soybean plants (Glycine max L. Merr) were grown with 100 p~ S and 15 mM N and studied with respect to S allocation during grain development. The grains accounted for 87% of the S taken up after d 42, the balance coming from internal redistribution of S from leaves and pods. Detailed studies of the leaves, pods, and grains associated with leaf axils 6 and 7 showed that sulfate accumulated in the pods as they expanded to 50% of full length, ahead of grain enlargement, but declined to very low levels as grain growth commenced. Conversely, homoglutathione (hCSH), cysteine, and methionine increased. In developing grains, hCSH accounted for 60 to 90% of the soluble-S but sulfate was barely detectable. The data are consistent with a model in which, under S-limiting conditions, the pods act as sinks for sulfate and grain growth initiates the assimilation of sulfate into hCSH in the pods, and then into developing grains, where it is incorporated into grain proteins.Mature soybean (Glycine max L. Merr) grains contain about 30 to 40 pmol S, almost entirely in the insoluble fraction, where it is associated with the seed-storage proteins (Sunarpi and Anderson, 1995). In generative plants under greenhouse conditions, the pods associated with each leaf axil typically contain about three to six grains in one or more pods, representing a total S demand of about 90 to 240 Fmol of S per axil during grain development. This compares with approximately 6 to 15 pmol of S for a typical mature leaf grown under S-sufficient conditions. In soybean it has long been known that hGSH occurs at a very high concentration in grains, leading to the suggestion that hGSH is an important source of S for grain development (Macnicol and Bergmann, 1984; Klapeck, 1988). However, with this exception, little is known about the internal and externa1 sources of S that are required to satisfy the very large demand for S in generative soybean, and there appears to be no information concerning the allocation of S and internal redistribution of S in generative plants. In this paper we address these questions as they apply to generative soybean. We report that the large demand for S during grain enlargement is associated with net loss of soluble S from the leaves and pods but that most of the demand for grain S is fulfilled by uptake of S during generative growth. Under the experimental conditions ' used, which can be viewed as being S-limiting, the data support a model in which S is imported into the pods mostly as sulfate, and is assimilated into hGSH before incorporation into the developing grains. MATERIALS A N D M E T H O D S Nomenclature for the Plant PartsThe terms L, P, and G are used to refer to leaves, pods, and grains, respectively, and are numbered according to the relevant leaf axil. Thus, L6 refers to leaf 6, P6 refers to the pods (usually two, Table I) in the axil of L6, and G6 refers collectively to the grains in the P6 pod(s). Growing ConditionsSoybean (Glycine max L. var Stephens) plants were raised during the summer in a greenhouse in sand:ver...

Abstract. Sunarpi, Jupri A, Kurnianingsih R, Julisaniah NI, Nikmatullah A 2010. Effect of seaweed extracts on growth and yield of rice plants. Nusantara Bioscience 2: 73-77. Application of liquid seaweed fertilizers on some plant species has been reported to decrease application doses of nitrogen, phosphorus, and potassium on some crop plants, as well as stimulating growth and production of many plants. It has been reported that there are at least 59 species of seaweeds found in the coastal zone of West Nusa Tenggara Province, 15 of those species weres able to stimulate germination, growth, and production of some horticultural and legume plants. This research aims to investigate the effect of seaweed extracts obtained from ten species on growth and production of rice plants. To achive the goal, seaweed (100 g per species) wasextracted with 100 mL of water, to obtain the concentration of 100%. Seaweed extract (15%) was sprayed into the rice plants during vegetative and generative stages. Subsequently, the growth and yield parameters of rice plants were measured. The results showed that extracts of Sargassum sp.1, Sargassum sp.2, Sargassum polycistum, Hydroclathrus sp., Turbinaria ornata, and Turbinaria murayana, were able to induce growth of rice plants. However, only the Hydroclathrus sp. extract could enhance both growth and production of rice plants.

Sunarpi and Anderson, J. W. 1997. Inhibition of sulphur redistribution into new leaves of vegetative soybean by excision of the maturing leaf. -Physiol. Plant. 99: 538-545.When soybean plants are pulsed with ["Sjsulphate, label is subsequently redistributed from the roots to the leaves. This confounds studies to measure the redistribution of label from leaves. Accordingly, soybean plants (Glycine max [L.] Merr. cv. Stephens) were grown in 20 [iM sulphate and a small portion of the root system (donor root) was pulsed with [-^'S]sulphate for 24 h. After removing the donor root, the plants were transferred into unlabelled solution, either without sulphate (S20^S0) or with 20 \xM sulphate (S20-^S20) (intact plants). Also at this time, the expanding leaf (L3) was excised from half of the plants in each treatment (excised plants). Immediately after the pulse, only ca 15% of the label occurred in the roots and ca 40% in the expanding leaf, L3, mostly in the soluble fraction. In intact S20->S20 plants, '^S-label was exported from the soluble fraction of L3, mostly as sulphate, whilst L4 and L5 imported label. Similar responses occurred in S20->S0 plants except that export of label from L3 was more rapid. Excision of L3 from S20->S20 plants inhibited labelhng of leaves L4-L6 but not total sulphur, whereas in S20-^S0 plants, excision of L3 inhibited the import of both total sulphur and ''S-label in leaves L4, L5 and L6. The data suggest that the soluble fraction of almost fully expanded leaves is an important reserve of sulphur for redistribution to growing leaves. The '"^S-label in the root system exhibited fluctuations consistent with its proposed role in the recycling of soluble sulphur from the leaves.

Soybean (Glycine max L.) plants were grown in nutrient solution containing 10 p~ sulfate and were treated at various times with [35Slsulfate for 48 h. Crowth was then continued in unlabeled solution. l h e sulfur content of each leaf increased rapidly until it was about 40% expanded; small, additional increases occurred until the leaf was about 70% expanded, after which the sulfur content decreased by about 50%. Leaves that were about 60 to