A crystalline inclusion in sieve element nuclei of Amsinckia: II. The inclusion in maturing cells

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Abstract
The compound crystalloids formed in sieve element nuclei of Amsinckia douglasiana A. DC. (Boraginaceae) during differentation of the cell become disaggregated during the nuclear breakdown characteristic of a maturing sieve element. The phenomenon occurs in both healthy and virus-infected plants. The crystalloid component termed cy, which is loosely aggregated, separates from the densely aggregated component termed ex and disperses. The cx component may become fragmented, or broken into large pieces, or remain intact after the cell matures. After their release from the nucleus both crystalloid components become spatially associated with the dispersed P-protein originating in the cytoplasm, but remain distinguishable from it. The component tubules of P-protein are hexagonal in transections and are somewhat wider than the 6-sided cy tubules. The ex tubules are much narrower than the P-protein or the cy tubules and have square transections. Both the P-protein and the products of distintegrated crystalloids accumulate at sieve plates in sieve elements subjected to sudden release of hydro static pressure by cutting the phloem. The question of categorizing the tubular components of the nuclear crystalloid of a sieve element with reference to the concept of P-protein is discussed.