Prof. Mayak Shimon
Professor Mayak passed away on 10.6.2014
1937 - 2014
Ph.D. 1972, Hebrew Univ.; Lect. 1975; Sen. Lect. 1978; Assoc. Prof.
1984; Prof. 1990.
Research Interests:
Carbohydrate metabolism in flowers. Microbe-plant interactions.
Post-harvest of cut flowers. Plant response to stress.
Research Projects:
1. Carbohydrate pool in flowers.
2. Effect of viral movement protein on carbohydrate distribution in
rose flowers.
3. Plant growth promoting Rhizobacteria.
Abstracts of Current Research:
Sink Activity in Flowers
Transient water stress is an integral part of postharvest handling of
cut flowers. It affects the continued growth of the petals, thus the
flowers fail to open or they open improperly. As a result the flowers
exhibit a poorer appearance and are considered of lower quality.
In response to transient water stress a marked rise in the
concentration of soluble sugars has occurred in rose petals Rosa
hybrida L. cv. Mercedes and in wax flowers Chamelaucium unicatum. In
parallel, a reduction in starch and fructan has occurred. However
detailed analysis revealed that the main source of carbohydrates was
due to transport of sugars from the leaves to the flower heads. This
suggests that sink activity of the flower heads acts to mobilize
carbohydrates between adjacent organs. And it plays an important role
in the response to stress.
Survey of the enzymes
Of the various enzymes involved in carbohydrate metabolism, the enzyme
sucrose synthase exhibited the largest change in response to water
stress. Two forms are of interest in the present studies. The first,
membrane bound, is acting in the pathway of the biosynthesis of
cellulose, the major component of cell wall. The second form is acting
in the cytoplasm in the pathway of the biosynthesis of starch. In the
process soluble carbohydrates are drawn into the petals, a result of an
increase in sink activity.
The sucrose synthase (SS) enzymes were detected and quantified on
immuno-blots for specific visualization of SS proteins. In response to
water stress a marked reduction in the content of both the membrane
bound and the soluble enzyme was observed. In addition, it was found
that in response to water stress a reduction in the apparent activity
of the enzyme was observed. At the same time, the stressed flowers
contained higher concentration of soluble carbohydrates. These findings
clearly indicate that the biosynthetic pathway of cellulose is
suppressed in response to water stress
Effect of viral movement protein on
carbohydrate distribution in petunia flowers:
Following infection of plants with a virus, mobilization of nutrients
to the point of viral invasion occurs. It was reasoned that
preferential expression of this protein in flowers may change the
pattern of carbohydrate distribution.
Research is progressing along two lines:
1. Evaluation of the carbohydrate distribution in leaves and flowers of
tobacco plants during the development of transgenic and control plants.
2. Developing an efficient protocol for transformation of petunia
plants. This will allow us to introduce the gene for the viral protein
into the plants. Petunia plants were chosen because they seem to be
suitable as an experimental model in studying mobilization between
adjacent organs (leaves and flowers). Petunia bears single large
flowers adjacent to large leaves. At this point in time transgenic
plants were produced using a general promoter CaMV35S. DNA analysis
confirmed the presence of DNA in the transgenic plants. In addition we
plan to transform plants using flower specific promoter. This will
allow differential expression of the protein in the flowers. The
consequences in terms of carbohydrate distribution will then be
evaluated.
Plant Growth Promoting Rhizobacteria
Conceptually, plant growth-promoting bacteria can have an impact on
plant growth and development in two different ways: indirectly or
directly. The indirect promotion of plant growth occurs when
these bacteria decrease or prevent some of the deleterious effects of a
phytopathogenic organism by any one or more of several different
mechanisms. On the other hand, the direct promotion of plant
growth by plant growth-promoting bacteria generally entails providing
the plant with a compound that is synthesized by the bacterium or
facilitating the uptake of nutrients from the environment.
Thus far we have demonstrated that application of specific bacterial
suspension stimulated rooting of bean plants and it enhanced the growth
of bean, pepper and tomato plants. We also tested combined applications
of bacteria and fertilizers. The added bacteria enhanced the growth of
plants supplied with a wide range of concentrations of the fertilizers.
This implies that plants can be grown with nutrients applied at a small
fraction of the amount of fertilizers presently used in agriculture.
Also, a reduction of pollution that is associated with agricultural
practices can be realized.
Transient water stress is common occurrence in growing plants.
Generally it retards growth and reduce yield. In this context we are
evaluating the effect of the bacteria on the resistance of plants to
water stress. A very large difference was observed between the
bacterial treated plants and the control plants. While the bacterial
treated plants, upon re-watering recovered and resumed active growth
the control plants lagged behind and remained stunted.
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