Due to their complex structure with several chiral centres important anticancer agents are still extracted from plants and not synthesized chemically on a commercial scale. Sustainable bioproduction of the compounds of interest may be achieved by plant in vitro cultures. Undifferentiated callus and suspension cultures, which can be cultivated in large bioreactors easily, very often fail to accumulate the compounds of interest, whereas shoot and root cultures as well hairy roots normally produce the same compounds as in the appropriate organs. The production of anticancer compounds, such as the alkaloids vinblastine, vincristine, paclitaxel (Taxol®), camptothecin, or the lignan podophyllotoxin, by plant in vitro cultures is reviewed. Taxanes can be produced in bioreactors using cell suspensions of various Taxus species with good yields; presently paclitaxel is produced on a commercial scale by Phyton Biotech (Germany). Camptothecin has low yields in suspension cultures of Camptotheca acuminata or Nothapodytes foetida (0.0003–0.01%), but a good production (0.1–0.3% dry wt) in root and hairy root cultures of Ophiorrhiza pumila, O. mungos and C. acuminata. Podophyllotoxin can be produced in cell suspension and root as well as hairy root cultures of Podophyllum and various Linum species up to 130 mg/l (Linum album cell suspensions); its derivative 6-methoxypodophyllotoxin is accumulated in hairy roots of L. persicum up to about 500 mg/l. The in vitro production of dimeric indole alkaloids in Catharanthus roseus has failed so far both in undifferentiated and differentiated in vitro cultures. In cases where in vitro cultures show good yields, they can be employed in biotechnology for the sustainable production of valuable products.

The effects of solar ultraviolet (UV)-B and UV-A radiation on the potential efficiency of photosystem II (PSII) in leaves of tropical plants were investigated in Panama (9°N). Shade-grown tree seedlings or detached sun leaves from the outer crown of mature trees were exposed for short periods (up to 75 min) to direct sunlight filtered through plastic or glass filters that absorbed either UV-B or UV-A؉B radiation, or transmitted the complete solar spectrum. Persistent changes in potential PSII efficiency were monitored by means of the dark-adapted ratio of variable to maximum chlorophyll a fluorescence. In leaves of shade-grown tree seedlings, exposure to the complete solar spectrum resulted in a strong decrease in potential PSII efficiency, probably involving protein damage. A substantially smaller decline in the dark-adapted ratio of variable to maximum chlorophyll a fluorescence was observed when UV-B irradiation was excluded. The loss in PSII efficiency was further reduced by excluding both UV-B and UV-A light. The photoinactivation of PSII was reversible under shade conditions, but restoration of nearly full activity required at least 10 d. Repeated exposure to direct sunlight induced an increase in the pool size of xanthophyll cycle pigments and in the content of UV-absorbing vacuolar compounds. In sun leaves of mature trees, which contained high levels of UV-absorbing compounds, effects of UV-B on PSII efficiency were observed in several cases and varied with developmental age and acclimation state of the leaves. The results show that natural UV-B and UV-A radiation in the tropics may significantly contribute to photoinhibition of PSII during sun exposure in situ, particularly in shade leaves exposed to full sunlight.

The present study tested with spinach (Spinacia oleracea L.), whether leaves are capable of long-term acclimative responses of carotenoids when warm-grown (20°C) plants were subjected to a regime of low temperature (1–6°C) and excess light (250 mol m–2 s–1). About 17 days after the temperature shift, leaves of the third leaf pair were compared with the respective leaves of warm-grown control plants. The cold-treated leaves exhibited reduced susceptibility to photoinhibition (at 4°C) and considerably faster kinetics of ‘recovery’ (at 20°C), as determined by changes in the ratio of dark-adapted variable to maximum chlorophyll fluorescence, FV/FM. The temperature shift induced marked changes in the composition of photosynthetic pigments. In particular, the pool of xanthophyll cycle pigments, viola-, anthera- and zeaxanthin, based on chlorophyll a+b, was enlarged by about 50%. The proportion of xanthophyll cycle pigments referred to the sum of carotenoids increased by about 25% and, in excessive light, a larger fraction of violaxanthin became deepoxidized. Overall, in respect of carotenoid composition and xanthophyll cycle activity, leaves that had been acclimated by temperature shift were very similar to leaves acclimated by growth in the field during autumn and winter. The data show that in spinach leaves, photoprotective mechanisms can be induced by temperature shift without requirement for development and growth at low temperature.

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A cell suspension culture of Taxus wallichiana (Himalayan Yew) was grown in shake flasks and a 20-L airlift bioreactor running for 28 days in a batch mode, and its capacity to accumulate paclitaxel and baccatin III was measured. When both culture types were in the highest productive state (from day 24 to day 28), there was a greater accumulation of paclitaxel and baccatin III in the bioreactor culture than in the shake flask culture (factor of 2.0 and 1.2, respectively). These increases in paclitaxel and baccatin III production cannot be related to the difference observed between the growth rates of both cultures, because when the bioreactor culture was at maximum productivity, its cell biomass, expressed in g L(-1) of dry weight, was similar to that obtained in the shake flask culture. It seems that these improvements were mainly due to adequate aeration and mixing of the culture in the bioreactor. The maximum yield observed for paclitaxel (20.84 mg x L(-1) day 24) and baccatin III (25.67 mg x L(-1) day 28) represents a productivity of 0.90 mg x L(-1) d(-1) and 0.93 mg x L(-1) x d(-1) respectively.