Gas Exchange Analysis of the Fast Phase of Photosynthetic Induction in Alocasia macrorrhiza1

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RESUMO

When leaves of Alocasia macrorrhiza that had been preconditioned in 10 micromoles photons per square meter per second for at least 2 hours were suddenly exposed to 500 micromoles photons per square meter per second, there was an almost instantaneous increase in assimilation rate. After this initial increase, there was a secondary increase over the next minute. This secondary increase was more pronounced in high CO2 (1400 microbars), where assimilation rate was assumed to be limited by the rate of regeneration of ribulose 1,5-bisphosphate (RuBP). It was absent in low CO2 (75 microbars), where RuBP carboxylase/oxygenase (Rubisco) was assumed to be limiting. It was therefore concluded that it represented an increase in the capacity to regenerate RuBP. This fast-inducing component not only gained full induction rapidly, but also lost it rapidly in low photon flux density (PFD) with a half time of 150 to 200 seconds. It was concluded that in environments with fluctuating PFD, this fast-inducing component is an important factor in determining a leaf's potential for photosynthetic carbon gain. It is especially important during brief periods (<30 seconds) of high PFD that follow moderately long periods (1 to 10 minutes) of low PFD.

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