Cytoplasm Exudate from Cut Phloem

Abstract

CYTOPLASM structure in sieve elements and particularly at sieve pores is of critical importance in any consideration of the translocation mechanism. The mass flow theory¹ assumes a degenerate sieve element protoplast in which vacuolar fluid fills the sieve element and is continuous through open sieve pores. A fluid flow of sucrose solution is thought to occur through sieve tubes due to an osmotic pressure gradient. Other theories propose that metabolic energy provides the motive force required to move nutrients over long distances through plants. These ‘active’ theories assume that the sieve elements have cytoplasmic contents similar to parenchyma cells but with exceptionally large end wall pores which are filled with cytoplasm. This interpretation is consistent with de Vries protoplasmic streaming theory², with Mason and Maskell's activated diffusion theory³, with Kursanov's molecular transfer theory⁴ and Spanner's electrokinetic theory⁵.