PHOTOPHYSIOLOGY OF TURION GERMINATION IN SPIRODELA-POLYRHIZA (L) SCHLEIDEN .11. STRUCTURAL-CHANGES DURING RED-LIGHT INDUCED RESPONSES

Germination response as well as de-etiolation (chlorophyll fluorescence in vivo), induced by irradiation with continuous red light (cR), were investigated in etiolated, photodormant turions of Spirodela polyrhiza. Structural changes during these physiological reactions were revealed by light and electron microscopy. Two different developed embryonic-like organs (frond primordia) were found and characterized in greater detail. One of the earliest cytological changes within these primordia after light-induction was the formation of dictyosomes, absent before cR irradiation. Enlargement of intercellular space during the first 48 h of cR irradiation pointed to cell elongation as the primary process on the cellular level. Cell division was demonstrated in the subsequent period (72 h cR) in parallel with the visible emergence of the new sprout. Disappearance of prolamellar bodies and formation of chloroplasts within the primordial cells was demonstrated before visible germination was detectable. The starch content of these plastids was increased within the pre-germination period, especially in apical cells. Therefore, carbohydrate translocation from the storage tissue to the frond primordia was postulated.