Involvement of polyamines in the chilling tolerance of cucumber cultivars

Abstract

The possible involvement of polyamines (PAs) in the chilling tolerance of cucumber (Cucumis sativus L. cv Jinchun No. 3 and cv Suyo) was investigated. Plants with the first expanded leaves were exposed to 3 degrees C or 15 degrees C in the dark for 24 h (chilling), and then transferred to 28 degrees C/22 degrees C under a 12-h photoperiod for another 24 h (rewarming). Chilling-tolerant cv Jinchun No. 3 showed a marked increase of free spermidine (Spd) in leaves, once during chilling and again during rewarming. Putrescine increased significantly during rewarming, but the increase of spermine was slight. Any of these PAs did not increase in chilling-sensitive cv Suyo during either period. PA-biosynthetic enzyme activities appear to mediate these differences between cultivars. Pretreatment of Spd to cv Suyo prevented chill-induced increases in the contents of hydrogen peroxide in leaves and activities of NADPH oxidases and NADPH-dependent superoxide generation in microsomes and alleviated chilling injury. Pretreatment of methylglyoxal-bis-(guanylhydrazone), a PA biosynthesis inhibitor, to chilled cv Jinchun No. 3 prevented Spd increase and enhanced microsomal NADPH oxidase activity and chilling injury. The results suggest that Spd plays important roles in chilling tolerance of cucumber, probably through prevention of chill-induced activation of NADPH oxidases in microsomes.

Figure 1

Changes with time of free PA contents in leaves of cv Jinchun No. 3 (upper) and cv Suyo (lower) during chilling and rewarming. Temperature and light conditions are indicated on top of the panels. Error bars indicate se (n = 3). ○, 3°C; ●, 15°C during chilling treatment.

Figure 2

Changes with time of PA-biosynthetic enzyme activities in leaves of cv Jinchun No. 3 (top) and cv Suyo (bottom) during chilling and rewarming. Enzyme activities in cv Suyo leaves during rewarming were not determined. Temperature and light conditions are indicated on top of the panels. Error bars indicate se (n = 3). ○, 3°C; ●, 15°C during chilling treatment.

Figure 3

Effect of 5 mm MGBG pretreatment to cv Jinchun No. 3, 2 h before chilling, on changes with time of free PA contents in chilled leaves during chilling and rewarming. Temperature and light conditions are indicated on top of the panels. Error bars indicate se (n = 3). ●, Pretreated with MGBG; ○, control (redrawn from Fig. 1).

Figure 4

Effect of 1 mm Spd pretreatment to cv Suyo, 12 h before chilling, on changes with time of NAPDH oxidation rate in 600 g of supernatants of leaf homogenate (A) and leaf hydrogen peroxide content (B) during chilling and rewarming. Temperature and light conditions are indicated on top of the panels. Error bars indicate se (n = 3). ●, Pretreated with Spd; ○, control.

Figure 5

NADPH oxidation (A and B) and NADPH-dependent superoxide generation (C) activities of cv Suyo leaf microsomes as affected by chilling with or without 1 mm Spd pretreatment. Microsomes were prepared 16 h after chilling (A and C) or 18 h after rewarming following chilling for 24 h (B). Error bars indicate se (n = 4).

Figure 6

NADPH oxidation activity of cv Jinchun No. 3 leaf microsomes as affected by chilling with or without 5 mm MGBG pretreatment. Microsomes were prepared 16 h after chilling. Error bars indicate se (n = 4).