Effect of Calcium on Sodium Salinization of Beans (Phaseolus vulgaris L.)

The efficiency of calcium in enhancing the tolerance of beans(Phaseolus vulgaris L.) to sodium salinization was studied inpot experiments in both cool and hot seasons. In the cool seasonincreased yields of dry matter, roots, nodules and pods werepositively correlated with increased Ca application and negativelycorrelated with the Na contents of irrigation water and planttissue. The Na levels both in roots and tops declined significantlyas increased amounts of calcium were added. Ca in the rangeof 2.0 to 8.0 mmol/1 caused competitive inhibition of Na uptakeand Na translocation. At Ca levels between 0 to 2.0 mM onlyNa translocation to tops was markedly inhibited. In warm seasonsCa had no beneficial effects on bean yields at any level ofNa. On the contrary, high rates of Ca application resulted ina higher death rate.     

Does Xylem Sap ABA Control the Stomatal Behaviour of Water-Stressed Sycamore (Acer pseudoplatanus L.) Seedlings?

Sycamore seedlings were grown with their root systems dividedequally between two containers. Water was withheld from onecontainer while the other container was kept well-watered. Effectsof soil drying on stomatal behaviour, shoot water status, andabscisic acid (ABA) concentration in roots, xylem sap and leaveswere evaluated. At 3 d, root ABA in the drying container increased significantly,while the root ABA in the unstressed container of the same plantsdid not differ from that of the control. The increase in rootABA was associated with the increase in xylem sap ABA and withthe decrease in stomatal conductance without any significantperturbation in shoot water status. At 7 d, despite the continuous increase in root ABA concentration,xylem sap ABA showed a marked decline when soil water contentwas depleted below 013 g g^–1. This reduction in xylemsap ABA coincided with a partial recovery of stomatal conductance.The results indicate that xylem sap ABA is a function of rootABA as well as the flow rate of water from roots to shoots,and that this ABA can be a sensitive indicator to the shootof the effect of soil drying. Key words: Acer pseudoplatanus L., soil drying, stomatal behaviour, xylem sap ABA     

Sodium and Cation Accumulation by Senna (Cassia acutifolia)

Senna plants, native to the arid parts of the northern Sudan,were analysed for mineral cations. Plants tended to accumulate salts in tops, particularly whengrowing in saline soils. Highest concentrations of salts (mostlyCa and Na) were in the leaves with a gradient from bottom totop leaves. Variation in the cation sum was associated withboth Ca and Na contents. Under high salinity, plant growth was reduced without injurysymptoms, but with shedding of some lower leaves. The same symptomswere also noted in plants subjected to soil moisture stress.It is therefore postulated that lower leaf shedding is a physiologicalmeasure for reducing plant salt level and transpiration.     

Acclimation to Drought in Acer pseudoplatanus L. (Sycamore) Seedlings

A glasshouse experiment was conducted with well-watered andwater-stressed seedlings of sycamore (Acer pseudoplatanus L.)grown in soil columns. Water was withheld when the seedlingswere 82-d-old. Effects of soil drying on stomatal behaviour,water relations, xylem cavitation, and growth of leaves androots were evaluated. Stomatal conductance declined well before any observable changein bulk leaf water potentials, and was correlated with soilwater status. At seven weeks, osmotic potential had declinedby 0·51 MPa and 0·44 MPa at full and zero turgor,respectively. Drought significantly increased both bulk elasticmodulus and leaf dry weight to turgid weight ratio of water-stressedplants. Drought had no effect on relative water content at zeroturgor. Water cavitation in the xylem was detected as ultrasonic acousticemissions (AE). Water-stressed plants displayed significantlyhigher rates of AE than well-watered plants. Maximum rate ofAE coincided with the minimum level of stomatal conductanceand apparent rehydration of the leaves. Drought caused changes in the root distribution profile andit increased the root weight. The increase in root weight wasmainly due to a substantial shift in assimilates allocated infavour of roots with total biomass being unaffected. Leaf growthwas maintained for six weeks without any significant declinein expansion rate. However, the development of severe waterstress reduced both leaf production and expansion.     

Some Primary Features of Salt Tolerance in Senna (Cassia acutifolia)

Studies on the germination of Cassia acutifolia (senna) seedsindicated, that they were highly tolerant of salinities up to16.0 mmhos cm^–1, and 50 per cent reduction in germinationoccurred, at about 20.0 mmhos cm^.1. Air temperature had a significanteffect on senna germination at substrate salinities between10.0 and 25.0 mmhos cm^–1. Seedling growth was more sensitive to salinity and alkalinitythan the germination stage. Young plant survival and total podyield were significantly reduced in soil salinities higher than11.0 minhoa cm^–1, and this was more pronounced when plantswere irrigated at short intervals with saline waters. The sensitivityof senna to higher levels of salinities was correlated withthe higher rate of chloride accumulation in the tissue resultingin specific chloride injury. However, the possibility of sodiuminjury cannot be excluded.