Effects of Sodium Chloride on Water Status and Growth of Sugar Beet

The effects of sodium chloride on the water status, growth,and physiology of sugar beet subjected to a range of soil waterpotentials were studied under controlled conditions. Sodiumchloride increased plant dry weight and the area, thickness,and succulence of the leaves. It increased the water capacityof the plant, mainly the shoot, but there was no evidence thatit altered the relationships between leaf relative water contentand the leaf water, osmotic, and turgor potentials or changedthe way stomatal conductance and photosynthesis responded todecreasing leaf water potential. The greater leaf expansionin sodium-treated plants is thought to be the consequence ofadjustments made by leaf cells to accommodate changes in ionsand water in a way that minimizes change in water and turgorpotentials. It is also suggested that the greater water capacityof treated plants buffers them against deleterious changes inleaf relative water content and water potential under conditionsof moderate stress.     

Calcium in the Root-hair Wall

The walls of normal root hairs of white mustard, corn and tomatoseedlings developed in moist air following seed treatment with⁴⁵CaCl₂, were tested by radioautography for incorporated calcium.Radioactivity was absent or faint over the growing tips butbecame concentrated immediately behind this point. It extendedback along the walls of the hairs, increasing in concentrationtowards the base. Since the hairs were subjected to plasmolysisand prolonged extraction with hot water prior to making theradioautographs, the distribution of radioactivity indicatedthe presence of bound ⁴⁵Ca. These findings are compatible withthe view that gradual calcification is essential for the normalgrowth and form of the hair. Radioautographs of mustard root hairs produced in an aqueoussolution of ⁴⁵CaCl₂ showed conspicuous radioactivity throughoutthe whole length of the hairs but particularly over the tips.Excessive wall calcification at the tips of these hairs couldbe the cause of their stunted growth.