Agricultural losses caused by salinity are difficult to assess but estimated to be substantial and expected to increase with time. Secondary salinization of agricultural lands is particularly widespread in arid and semiarid environments where crop production requires irrigation schemes. At least 20% of all irrigated lands are salt-affected, with some estimates being as high as 50%. Whereas the world's population continues to rise, the total land area under irrigation appears to have leveled off. The need for increased food production therefore needs to be met by increases in yield per land area. To reach this goal, genetic engineering of crop plants for enhanced salt tolerance will be a very important approach. In dry regions where fresh water becomes a scarce commodity, irrigation of moderately salt tolerant crops with brackish water is feasible. Transgenic lines of some crop species have been generated which can grow and develop at fairly high salinity levels in controlled environments. These transgenics must be tested vigorously for yield potential under field conditions.

No abstract

SummaryAn analysis of the rate at which isotope diffuses out of disks of beetroot tissue shows that there are at least two components of the non-free space. As tlwse components are not due to differences in cell type within the tissue, it is suggested they are due to a cytoplasmic phase in the parenchymatou's cells, and to the vacuoles.Evidence is given to support the suggestion that, as in the characean cell, these phases are in a series with the free space, so that ions pass to the vacuole in salt uptake through the cytoplasmic phase.Using this serial model for the cell it has been estimated from the amount of isotope diffusing out of labelled tissue that the cytoplasmic phase contains about 3 m-equivjkg K+ or Na+, and 0-1-1·0 m-equivjkg Br-, when the tissue is brought to equilibrhun with potassium or sodium bromide solution whose concentration is 10-50 m-equiv/l. The time for 50% exchange of K+ in this phase is about 2 hr at 2°0, and for Br-about 40 min. At 25°0 the exchange of both K+ and Br-is some three times faster.The fluxes into and out of the cell hiwe been estimated for K+ and Br-when either the concentration in the -solution or the content of the vacuoles was varied. It was shown that "salt saturation" of the tissue was mainly due to an increase in efflux as concentration in the vacuole increased. The permeability of the boundaries of the cytoplasmic phase to I{+, estimated from the fluxes, was about 10-8 em/sec, and it is suggested these boundaries are due to the plasmalemma and the tonoplast membranes respectively.

No abstract

No abstract