Figure 4.

The effect of increasing drought stress on soluble acid invertase activity (A) and insoluble acid invertase activity (B) at five different stages of ear development. A unit of enzymatic activity (U) equals 1 μmol of Suc hydrolyzed per minute under the assay conditions described in “Materials and Methods.” Legend as for Figure 1. F-tests and comparison of means for each stage were performed with the Gabriel-algorithm as described in caption for Table I (n = 3–4). Aggregate statistical analyses for the entire period showed that soluble acid invertase activity (A) was significantly lower under severe stress (t₃ and t₄) than in control (t_c) and moderate stress (t₁ and t₂). Paired t-tests showed that soluble acid invertase activity (A) was significantly higher (α ≤ 0.05) than insoluble acid invertase activity (B) on −6 d, −4 d, 0 d, and +3 d and significantly lower on +7 d.