Carbon Dioxide Photoassimilation in Normal-leaved and Mutant Forms of Pisum sativum L.

The reproducible steady-state carbon dioxide (CO₂) photoassimilationpotentials of three mutants and a normal form of pea (Pisumsativum L.) have been compared. The three mutants studied differed markedly in foliar morphology:genotype af af Tl Tl had leaflets converted to tendrils; AfAf tl tl had tendrils converted to leaflets; af af tl tl hadrelatively minute leaflets on a branched petiole. Interest layprimarily in the phenotype with only tendrils since it provideda potential means of reducing the volume of haulm that has tobe rapidly processed in the case of vining peas, and dried inthe case of harvest peas. These mutants had been derived from relatively unimproved cultivars.Before completion of the lengthy backcrossing required to makea full assessment of the value of such mutants an interim studyusing infra red gas analysis indicated that, in terms of CO₂ photoassimilation perunit area of youngest expanded attached leaf of glasshouse-grownplants, the mutants were comparable to normal. The phenotypewith only tendrils was the least efficient of those assayedat utilizing light of an intensity below 100 J m² sec¹ (400–700nm), and on a unit dry-weight basis it was only 18 per centas efficient as a normal-leaved pea. The other mutants werecomparable to normal in this respect. Comparison of CO₂ photoassimilation of glasshouse-grown andfield-grown plants showed them to be similar though they differedin dry weight, transpiration, and dark respiration.