Phase Change in Citrus: Immunologically Detectable Differences Between Juvenile and Mature Plants

Abstract

Homogenates prepared from mature and juvenile grapefruit (Citrus paradisi Macf. cv. Marsh) were used to raise antibodies in rabbits. The resultant polyvalent antisera were subjected to immunoadsorption and selection techniques. A specific antiserum was obtained which reacted with an antigenic protein found in greater quantities in tissues of mature Citrus plants than in tissues of juvenile plants. This is referred to as the 'mature' protein. The 'mature' protein is resistant to temperatures of up to 80ºC, and has a molecular weight of approximately 59.7 kDa. The protein is found in Citrus species, but not in the closely related genera Poncirus, Microcitrus or Fortunella. It is not found in the other plant species studied. The mature protein content increases in the leaves towards the apex of single-stemmed seedlings, and in the floral shoots of precociously flowering Marsh grapefruit seedlings. There are few morphological or chemical characters which change concurrently with the achievement of maturity in citrus seedlings, and none is well suited as a predictor of phase change. The identification of a protein marker associated with phase change has important implications, both in the understanding of the processes of phase change, and in the practical field of plant breeding.