Soil salinity is a major factor affecting crop productivity worldwide. This study explores mechanisms that contribute to salt tolerance in rice (Oryza sativa L.). Hydroponically grown, 2‐week‐old salt tolerant and sensitive indica rice varieties, Pokkali and Jaya, respectively, were exposed to a 48‐h stress period with NaCl (0–250 mM). When exposed to 200 mM NaCl, micromolar levels of external Ca2+ elevated survival of both varieties. The Ca2+ levels required were lower for Pokkali than for Jaya, but resulted in significantly higher survival. Estimates of Na+ and K+ in root and shoot compartments were made by flame photometry, while X‐ray microanalysis was used to localize Na+ in the extracellular matrix of the shoot. Transpirational bypass flow was estimated using the apoplastic tracer, 8‐hydroxypyrene‐1,3,6‐trisulphonic acid, trisodium salt. Our data demonstrate a Ca2+‐dependent reduction in Na+ transport to shoots, which correlated with a decline in bypass flow and of Na+ in the transpirational stream. In addition, the Na+ that enters the shoot is partitioned among several distinct compartments. Survival is inversely correlated with Na+ levels in the shoot apoplastic fluid, which surrounds the cell and influences cytosolic composition. Pokkali maintained lower Na+ in its apoplast compared with the salt sensitive Jaya at the same total shoot Na+. Na+ in the apoplast appears to be regulated by sequestration into intracellular compartments. This sink supplements the primary response of reducing Na+ influx into the shoot and effectively buffers the apoplastic fluid in Pokkali. All of these mechanisms are operational in Jaya as well but are deployed less effectively.

Crop yield is a highly complex quantitative trait. Historically, successful breeding for improved grain yield has led to crop plants with improved source capacity, altered plant architecture, and increased resistance to abiotic and biotic stresses. To date, transgenic approaches towards improving crop grain yield have primarily focused on protecting plants from herbicide, insects, or disease. In contrast, we have focused on identifying genes that, when expressed in soybean, improve the intrinsic ability of the plant to yield more. Through the large scale screening of candidate genes in transgenic soybean, we identified an Arabidopsis thaliana B-box domain gene (AtBBX32) that significantly increases soybean grain yield year after year in multiple transgenic events in multi-location field trials. In order to understand the underlying physiological changes that are associated with increased yield in transgenic soybean, we examined phenotypic differences in two AtBBX32-expressing lines and found increases in plant height and node, flower, pod, and seed number. We propose that these phenotypic changes are likely the result of changes in the timing of reproductive development in transgenic soybean that lead to the increased duration of the pod and seed development period. Consistent with the role of BBX32 in A. thaliana in regulating light signaling, we show that the constitutive expression of AtBBX32 in soybean alters the abundance of a subset of gene transcripts in the early morning hours. In particular, AtBBX32 alters transcript levels of the soybean clock genes GmTOC1 and LHY-CCA1-like2 (GmLCL2). We propose that through the expression of AtBBX32 and modulation of the abundance of circadian clock genes during the transition from dark to light, the timing of critical phases of reproductive development are altered. These findings demonstrate a specific role for AtBBX32 in modulating soybean development, and demonstrate the validity of expressing single genes in crops to deliver increased agricultural productivity.

Rice (Oryza sativa L.), a staple food in Asia, is very sensitive to soil salinity. However, intraspecific variations exist, with the coastal cultivar Pokkali tolerating even brackish water. This study explores cellular mechanisms that contribute to salt tolerance in rice. It is widely accepted that limiting cytosolic Na 1 should improve the survival of plants subjected to saline stress. However, an understanding of the mechanisms by which Na 1 levels are controlled in relatively tolerant cultivars requires monitoring cytosolic Na 1 non-invasively and in real time, which is technically challenging. We have used two-photon excitation for the ratiometric estimation of cytosolic Na 1 in cultured cells using sodium-binding benzofuran isophthalate. Pokkali cells maintained low cytosolic Na 1 (approximately 25 mM), and a viability of over 85% under high salinity , while Jaya cells were unable to maintain low cytosolic Na 1 and suffered decreased viability even at moderate saline stress. Here we show that the permeability of the Pokkali plasma membrane to Na 1 is significantly lower than that of Jaya, to the extent that it is comparable with permeabilities reported for halophytes. Pokkali effectively sequesters Na 1 in intracellular compartments utilizing a Ca 21 -regulated transport system(s). Together these cellular mechanisms allow Pokkali to maintain low cytosolic Na 1 up to a stress of 250 mM NaCl. The findings demonstrate that differences in survival between these contrasting varieties of rice are mainly because of differences in membrane transport mechanisms and thus have significance in crop improvement.

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Western-blot analysis and protein kinase assays identified two Ca 2؉ -dependent protein kinases (CDPKs) of 55 to 60 kD in soluble protein extracts of embryogenic cultures of sandalwood (Santalum album L.). However, these sandalwood CDPKs (swCDPKs) were absent in plantlets regenerated from somatic embryos. swCDPKs exhibited differential expression (monitored at the level of the protein) and activity in different developmental stages. Zygotic embryos, seedlings, and endosperm showed high accumulation of swCDPK, but the enzyme was not detected in the soluble proteins of shoots and flowers. swCDPK exhibited a temporal pattern of expression in endosperm, showing high accumulation and activity in mature fruit and germinating stages; the enzyme was localized strongly in the storage bodies of the endosperm cells. The study also reports for the first time to our knowledge a post-translational inhibition/inactivation of swCDPK in zygotic embryos during seed dormancy and early stages of germination. The temporal expression of swCDPK during somatic/zygotic embryogenesis, seed maturation, and germination suggests involvement of the enzyme in these developmental processes.