In many crop species, supplemental Ca2l alleviates the inhibition of growth typical of exposure to salt stress. In hydroponically grown cotton seedlings (Gossypium hirsutum L. cv Acala SJ-2), both length and weight of the primary root were enhanced by moderate salinities (25 to 100 millimolar NaCQ) in the presence of 10 millimolar Ca2", but the roots became thinner. Anatomical analysis showed that the cortical cells of these roots were longer and narrower than those of the control plants, while cortical cells of roots grown at the same salinities but in the presence of only 0.4 millimolar Ca2" became shorter and more nearly isodiametrical. Cell volume, however, was not affected by salinities up to 200 millimolar NaCl at either OA or 10 millimolar Ca2". Our observations suggest Ca2-dependent effects of salinity on the cytoskeleton. The rate of cell production declined with increasing salinity at 0.4 millimolar Ca21 but at 10 millimolar Ca2@ was not affected by salinities up to 150 millimolar NaCI.salt-resistant crop species, is, nonetheless, fairly salt-sensitive during the seedling stage (20). Supplemental Ca reduced Na+ influx, improved K+/Na+ selectivity and actually stimulated root growth at salinities up to 150 mM NaCl (GR Cramer, unpublished data;6,14); furthermore, it seemed to improve the resistance of the roots to microbial attack (20 and references therein).The Ca2" level of the medium also influenced the morphology of salt-stressed roots: roots grown in the presence of 10 mm Ca2"were not only longer but also thinner than roots grown in 0.4 mM Ca2? (6). This raised the question whether the observed changes in growth were mediated through changes in cell size, the rate of cell production, or both (29, 34). We here report that salinities up to 150 mm NaCl affect cell production only when Ca2" levels are relatively low. The three-dimensional shape of root cells, but not cell volume, is also differentially affected by salinity depending on the external Ca2" concentration, which suggests direct or indirect effects of Na+ and Ca2" on the cytoskeleton.Most crop plants suffer a decline in growth when exposed to saline conditions. The deleterious effects of salinity are thought to result from water stress, ion toxicities, ion imbalance, or a combination ofthese factors. One ofthe requirements for growth is maintenance ofcell turgor above a threshold level; under saline conditions, osmotic withdrawal of water from enlarging cells may cause their turgor pressure to drop below the threshold.Unless the plant can generate a sufficiently negative osmotic potential to reverse the flow of water, either by uptake of ions from the medium or by synthesis of organic osmotica, growth will stop. Ion imbalances in plants can, for example, occur when high concentrations of Na+ in the soil reduce the amounts of available K+, Mg2", and Ca2" (10) or when Na+ displaces membrane-bound Ca2+ (7). Sometimes Na+ has direct toxic effects, as when it interferes with enzyme structure and function. It may also interfere with the fun...

Roots of Marsilea vestita ranging from 1–120 mm in length, as well as root primordia, were analyzed to determine mitotic activity and ploidy levels in the apical cell, five well‐defined regions of the root proper, and two regions in the root cap. The mitotic index of the apical cell tended to be above the overall mean mitotic index for the entire apical meristem. No diurnal rhythm in mitotic index was apparent. The cell‐cycle duration of the apical cell ranged from 12.1–25.2 hr, that of other regions of the root from 16.1–41.5 hr. There was no indication of polyploidy in any part of the apical meristem except in a few procambial cells. Thus, the results support the classical concept that the apical cell is the ultimate source of cells in the root.

Seeds of Lyeopersicon esculentum cv. VF36 (a salt‐sensitive cultivar), L. esculentum var. Edkawi (which is fairly salt‐resistant), and a wild relative, L. cheesmanii, were exposed to various concentrations of NaCl, up to 460 mol m−3, either directly or following imbibition in non‐saline nutrient solution. After 10 d exposure to salt, they were transferred to non‐saline solution. All taxa showed some germination at the lowest salinity tested, 92 mol m−3 NaCl, but virtually no germination occurred at 184 mol m−3 NaCl or higher salinities. Within 2 d after removal of the salt stress, however, the seeds of L. esculentum reached control levels of germination, even if they had already been on the verge of germination when the stress was imposed. The seeds of L. cheesmanii were less resistant to NaCl. The physiological basis for the resistance of VF36 seeds is discussed.

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The DNA content of the apical cell and various other cells in the roots of Azolla filiculoides was determined by two‐wavelength cytospectrophotometry. DNA content decreased markedly with increasing age of the apical cell; there was a similar but less pronounced trend in the other cell populations studied. These findings suggest the possibility of DNA amplification in very young roots with rapidly dividing cells.