The effect of photoautotrophy on photosynthesis and photoinhibition of gardenia plantlets during micropropagation

We studied the relationships between the degree of photoautotrophy, photosy nthetic capacity, and extent of photoinhibition of Gardenia jasminoides Ell is plantlets. in vitro. Two successive micropropagation stages (shoot multi plication and root induction), and three culture conditions [tube cap closu re, photosynthetic photon flux density (PPFD), and sucrose concentration] w hich may influence the development of photoautotrophy in vitro were assayed . The ratios of variable chlorophyll fluorescence to either maximal (F-v/F- m) or ground (F-v/F-0) values were low, irrespective of the culture stage o r growing conditions. Incomplete development of the photosynthetic apparatu s and permanent photoinhibition may be involved. However, F-v/F-m and F-v/F -0 increased from shoot multiplication to root induction owing to a decreas e in F-0 and an increase in F-m. This suggests that photoinhibition decreas es later during micropropagation, when the photoautotrophy of plantlets is more advanced. The low sucrose content and high PPFD increased the photoinh ibition of plantlets, whereas growth in tubes with permeable caps showed th e opposite effect. The only culture factor with a significant (positive) ef fect on maximum photosynthetic rate (P-max) was PPFD. At shoot multiplicati on net photosynthetic rate (P-N) was positively correlated with the half ti me of the increase from F-0 to F-m (t(1/2)). Such association may be mainly due to a common response of both traits to higher PPFD in culture. Within each culture stage, no relationship was observed between P-N and the degree of photoautotrophy, which was positively correlated with F-v/F-m and F-v/F -0 during root induction. During shoot multiplication, these correlations w ere not significant, or were even negative. Hence during the last stage of micropropagation, plantlets with a higher degree of photoautotrophy are les s photoinhibited, whereas they do not follow this pattern at the earlier st age.