In: Biology
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How do angiosperms seal off wounded sieve tube elements to prevent bleeding? Describe the short-term and long-term mechanisms?
Callose is deposited into the tangled mass in the sieve pores of damaged sieve tubes, which serves to seal off the damaged sieve elements. Callose proliferates when there is a pressure drop, which helps to seal the sieve pores.
The sieve-tube elements of long-lived arborescent monocotyledons which lack secondary thickening remain functional for many decades despite lacking a nucleus. A minimal requirement for transport by mass flow powered by the Munch mechanism is maintenance of semi-permeability of the plasmalemma of the sieve tube elements; loading and re-loading could be deputed to nucleate cells symplastically linked to the sieve elements. An additional requirement in the long-term relates to replacement of components damaged by mechanical, chemical or radiation intrusions. Minimizing the damage from radiation and chemical agents can be related to a number of commonly observed features of sieve tubes.