Responses of tomatoes with different resistance to heat stress: Cytochemical investigation of some
oxidoreductases in pollen
Georgieva, I., Kruleva, M., Danailov, Zh., Krapchev, B.
Institute of Genetics, Bulgarian Academy of Sciences, Sofia 1113
Research on plant resistance to temperature stress is of special practical interest, as the improvement of
crop plants involves the improvement of their resistance to extreme temperatures. There is convincing evidence
that variation in sporophyte responses to temperature is expressed in the gametophyte (Polito, Weinbaum, 1992)
which provides the opportunities to carry out the gametophyte selection for resistance using pollen test (Zamir,
Gadish, 1987). Tomato is a conventional object for pollen selection.
The primary intent of the present study is to evaluate the dependence between the resistance of tomato
plants to heat stress and changes in the pollen metabolism associated with the metabolic pathways of glucose
catabolism. Besides comparison of metabolic changes in the pollen grains and pollen viability was made.
Tomato seedlings from lines 502 and 498 and as well as from their hybrid were subjected to high
temperature stress in a climatic camera at 42°C for 6 hours. Following treatment the plants were turned back to
25°C. The plant resistance expressed as the degree of increase in seedling length for every genotype of treated
and control variants was determined (Udovenko, 1988). The effect of high temperature on the pollen metabolism
was investigated after treatment of the flowering tomato plants from the same lines for 48 hours at 42°C/28°C
(day/night) and photoperiod 16/8 hours (day/night).
Activities of some oxidoreductases involved in different respiratory pathways were studied cytochemically.
Cytochromoxidase (Cyt oxidase) activity was proved by using NADI-reaction. Dehydrogenases - isocitrate
dehydrogenase (I DH), glutamate dehydrogenase (GDH), alcohol dehydrogenase (ADH) and lactate
dehydrogenase (LDH) were localized by the method of tetrazolium reductases. Peroxidase (POD) was studied by
the method of Graham & Karnovski (Lojda et al., 1979).
The pollen viability was substantiated with the fluoro-chromatine test (FCR) (Heslop-Harrison et al., 1984).
It was established that the female parent - line 502 expressed higher heat resistance, the male parent -
line 498 was susceptible to heat stress whereas the hybrid showed intermediate heat resistance. The heat
treatment decreased pollen viability in the same manner as the seedling length (Fig.1). The reduction of pollen
viability was associated with depressed aerobic respiration (reduction of cytochrome route), probably suppression
of short respiratory chains where POD is implicated taking part (Rubin, Ladygina, 1974) as well as with increase of
anaerobic glycolysis (ethanolic and lactate fermentation) (Fig.1).
A coincidence of data for the parental line resistance to heat stress with the results from the cytochemical
study of pollen was observed. However, the pollen of the hybrid showed lower IDH and GDH activities and higher
LDH activity than these values of both parental lines (Fig. 1).
Having in mind that glycolytic network may provide an essential metabolic flexibility that facilitates plant
adaptation to environmental stresses (Plaxton, 1996) the observed drastic increase of LDH activity in the hybrid
pollen probably supports the possibility of the hybrid for faster overcoming of negative effects of the heat stress.
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