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Cucurbit Genetics Cooperative Report 21:16-17 (article 6) 1998

Free Proline Contents and Catalase Activity in Cucumber Leaves at Elevated Temperatures

Meng Zhang, Hongwen Cui and Sheng Zhao

Department of Horticulture, Northwestern Agriculture University, Yangling, Shaanxi, 712100, P.R. China

Introduction. Heat tolerance of cultivars in cucumber is a very important character for mid-summer and early autumn production in north China (1,2). If one could distinguish the tolerance of cultivars nd breeding lines by an index measure at some developmental stage, phenotypic selection could be possible. The purpose of our research was to identify a physiological index associated with heat tolerance in cucumber.

Materials and Methods. Five cultivars with different heat tolerance sensitivities were selected, [Erzaozi (no. 1), Heidan-1 (No. 2), 8113 (No. 3), Jin-4 (No. 4) and 3511 (No. 5)] in order to study heat tolerance. Plants of each cultivar cultured 25 days in the three-leaf stage were heat treated at the temperature of 36 C and compared to control plants grown at 28 C. The free proline concentration and the activity of catalase in treated and controlled leaves of each cultivar were measured after 1 day, 3 days, and 5 days. Relative increment percentage (RIP) indicated relative plant reaction under heat stress and was calculated as:

RIP =
[(contents/activity at 36 C) - (contents/activity at 28 C)]
(contents/activity at 28 C )
X 100

Results.

1. Free proline contents in leaves. The RIP of each cultivar after 1, 3, and 5 days is shown in Table 1. The positive sign of all RIP values indicates that the contents of free proline in leaves accumulated after heat-treatment. Generally, RIP increased first and reached its maximum after 3 days under heat-treatment, and then decreased after 5 days. At Days 1 and 5 after heat treatment, the RIP of heat-tolerant cultivars No. 5 and No. 1 was evident. At Day 3 the RIP of cultivars was variable and the RIP of cultivar No. 5 was highest, followed by cultivar No. 4 and No. 3. The RIP of cultivar No. 1 was lowest and RIP of cultivar No. 2 was slightly higher than that of No. 1. The more tolerant the cultivar was, the higher the observed RIP value. The RIP of free proline after 3 days of heat treatment was discriminating, and coincided completely with the heat tolerance ranking other cultivars examined.

2. Activity of catalase. The RIP of each cultivar is shown in Table 2. Data revealed that catalase activity decreased after 1 day of heat treatment, and the decrease in RIP of heat tolerant cultivars No.5 and No.4 was less than the other cultivars tested. Activity was restored gradually after Days 3 and 5 with the exception that cultivar No.4 which decreased again after 5 days of treatment. These results show that the heat tolerance of the cultivars examined was not consistent.

Table 1. RIP of free proline contents in cucumber leaves subjected to heat stress (%).

Cultivars
Treatment
No. 1
No. 2
No. 3
No. 4
No. 5
After 1 day
3.9
18.5
40.9
74.5
55.0
After 3 days
74.3
95.0
655.0
673.0
953.2
After 5 days
13.8
117.5
122.0
129.3
142.8

Table 2. RIP of catalase activity in cucumber leaves subjected to heat stress (%).

Cultivars
Treatment
No. 1
No. 2
No. 3
No. 4
No. 5
After 1 day
-93.1
-93.2
-55.2
-11.8
-49.7
After 3 days
-44.1
-81.7
-31.5
105.5
-9.7
After 5 days
13.8
46.1
109.7
43.7
209.5

Literature Cited

  1. Zhang, Fusuo. 1993. Environment adversity and plant nutrient. Beijing Agricultural University Publishing House.
  2. Zhao, Kefu. 1990. Physiology of Plant Resistance. Agriculture Publishing House.
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Page citation: Wehner, T.C., Cucurbit Genetics Cooperative;
Created by T.C. Wehner and T. Ng, 1 June 2005; design by C.T. Glenn;
send questions to T.C. Wehner; last revised on 15 December, 2009