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Summary
Pepper (Capsicum annuum) is a thermophilic species and is very sensitive to low night
temperatures where the vegetative and reproductive development are affected. The
compensation method, which constitutes the basis of this work, is based on the idea that
plant exposure to moderate heat stress during the day will activate defense mechanisms
against the low night temperatures of the winter.
The pollen is the plant's most sensitive organ to abiotic stresses. Very little is known
about defense mechanisms against stress in developing pollen grains. Heat shock proteins
are related to maintaining the conformation, prevention sedimentation and aggregation of
proteins in response to the exposure to heat stress or other abiotic stresses. These proteins
may also be involved in the defense mechanisms of the developing pollen grains.
In order to find out the role of heat shock proteins, in the defense against cold stress in
pepper, their expression profile was examined in leaves of young plants, following a heat
treatment.
In addition, the expression profile was examined in pollen and leaves of mature plants,
exposed to higher day temperatures. As controls, plants were exposed to optimal
conditions (high night temperatures) or to non heating conditions during day or night.
In contrast to the common opinion that pollen is lacking in expression of Hsp's, the
results of this study indicates that Hsp's are induced by exposure to compensation
treatments.
Organelles' sHsp's, Hsp70 and Hsp60 were induced in pollen grains, following their
exposure to heat treatments of the compensation method.
In leaves, organelles' sHsp's and Hsp60 were induced during the compensation
treatments.
Differences in the Hsp's expression profiles have been observed between the young
leaves from young or mature plants. For example the induction of Hsp70 due to the
exposure to heat which occurred in leaves of young plants but not of mature plants or the
expression of sHsp class I in young plants but not in mature plants.
There is a correlation between Hsp's expression in leaves and pollen and between the
positive effects of the compensation treatments on the plants, which can indicate on
possible involvement of Hsp's at this mechanism, but not at unequivocal way. The heat
response network at cells is very complex and it will be very interesting to learn more
about additional factors, which are involved in this mechanism. In future, it will be
feasible to explore the expression profile of plant hormones, Hsf's and APX, since there
is a cross - talk between different abiotic stresses.