Effect of Potassium Deficiency on C3 and C4 Cereals

C₄ cereals (Zea maya L. and Sorghum bicolor L. Moench) and C₃cereals (Triticum aestivum L. and Hordeum vulgare L) were grownin nutrient solutions with constant, interrupted, or absentpotassium supply. The lack of potassium retarded shoot growthand depressed the chlorophyll accumulation in all species ina similar way. After the renewal of potassium, the differencesin the compensation for growth retardation were not correlatedwith the photosynthetic system, but with the recovery of chlorophyllaccumulation in younger leaves. As important for the compensationof shoot growth retardation was a slower senescence of old leavescompared to plants with a constant potassium supply. This wasshown by the chlorophyll content and PEP carboxylase activity.In contrast to C₃ cereals, the C₄ cereals did not react withhigher chlorophyll contents to the same extent after the renewalof the postassium supply. The PEP carboxylase activity, however,was immediately raised higher than in control leaves. Chlorophylland PEP carboxylase activity increased simultaneously only inless aged leaves.