AGGLUTINATION OF MESOPHYLL PLASTIDS AND OBLITERATION OF PHLOEM SIEVE TUBES
ARE THE TOTAL RESULT OF SEASONAL PAUSES IN PHOTOSYNTHATE EXPORT
Yu. V. Gamalei
V. L. Komarov Botanical Institute RAS, St. Petersburg, 197022;
e-mail: ygamalei@mail.ru
Chloroplast agglutination and sieve tube obliteration are related to the different plant tissues: the agglutination
— to the leaf mesophyll, and the obliteration — to the axis phloem. Being equally produced by photosynthate
export dynamics, both phenomena are synchronous and can be used for diagnostics of seasonal flashes and
pauses of photosynthetic activity with equal success. The nature of the mobility of chloroplast and their shuttle
displacements from the nuclear envelope to the cell periphery connected with export dynamics have been established.
It is assumed that nuclear envelope is the base structure of the endoplasmic reticulum (ER) inside which
the chloroplasts are localized. Activation of photosynthesis and sugar accumulation inside the ER induces its
expansion followed by centrifugal diffusion of chloroplasts. Come back effect — ER collapse, its return to the
source — can be induced by the blockade of photosynthesis. Centripetal collapse is accompanied by plastid
concentration around the nuclear envelope. Displacements of ER and the chloroplasts dislocating inside it are
reversible. It depends on seasonal fluctuations of photosynthesis and export intensities. Changes in the volume
of sieve tubes, which are due to the same reason, are irreversible. Each seasonal wave of photosynthesis and sugar
export forms new series of sieve tubes, replacing obliterated ones.
Key words:
plastids, endoplasmic reticulum (ER), cytoskeleton, mobility, photosynthesis, photosynthate
export, sieve tubes, agglutination, obliteration
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