Causes of Growth Reduction in Elongating and Expanding Leaf Tissue of Sugarcane Under Saline Conditions

Abstract

Plants of sugarcane, cv. Co 1148, were subjected to salinisation with 200 milliequivalents L^-1 of Cl^- -type salts mixture (having Na⁺, Ca²⁺ and Mg²⁺ as 3 :1:1 and Cl^- and SO₄^2- as 4:1 on a milli- equivalent basis) for two weeks or more during the tillering phase. Soluble sugar concentrations increased by 55% in the blades of recently matured leaves (source tissues) and by nearly 225% in the elongating sheath bases (sink tissues) as a result of salinisation. Leaf elongation within 3 h of desalin- isation was much faster than for the non-saline controls. The accumulated sugars also dropped in the rapidly elongating sheath bases by 43% during this period after desalinisation. Further, the drop in sugar levels upon desalinisation was of greater magnitude in the more rapidly growing sheath bases. The present studies indicate that even though the supply of carbohydrates from the source tissues is reduced, the sink tissues are not able to make use of these sugars under saline conditions. As Na⁺ and Cl^- concentrations did not change within 3 h of desalinisation, the ions themselves did not appear to affect metabolic activities of the sink tissues; this suggestion is further supported by the utilisation of accumulated sugars within 3 h of desalinisation.