Variation in preleptotene chromosome contraction among three cultivars of Lilium longiflorum

Preleptotene chromosome contraction was observed in several clones of Lilium longiflorum cultivars Ace, Nellie White and Croft. The degree of chromosome contraction was variable, among microsporocytes of single anthers, buds of individual plants, and clones of single cultivars. It is suggested that one of the sequence of genetically controlled events that determine the orderly development of meiosis provides for the temporary inhibition of mitotic coiling, thus allowing the development of leptotene; and if this gene action is delayed or out of sequence, a period of mitotic-like chromosome contraction precedes leptotene. These cultivars appear to share an inherited predisposition for such an irregularity in sequence of gene action. Differences between clones may be attributed to differences in other genes affecting these earliest stages of meiosis. There is some evidence of external environmental influence upon this genetic predisposition for preleptotene chromosome contraction, that is, there appears to be an inverse correlation between degree of preleptotene contraction and temperature. The degree of chromosome contraction may also be influenced by different metabolic conditions affecting microsporocytes developing sequentially in the anther. Experiments are presently underway to determine whether the degree of preleptotene chromosome contraction is related to chiasma frequency.