| 释义 |
plastochron Bot.|ˈplæstəkrɒn|
Also -chrone |-krəʊn|.
[a. G. plastochron (E. Askenasy 1878, in Verhandl. des Natur-hist.-med. Vereins zu Heidelberg II. ii. 76), f. Gr. πλαστό-ς formed, moulded (see -plast) + χρόν-ος time.]
The interval of time between consecutive formations of leaf primordia (or of pairs of such primordia) in a growing shoot apex of a plant.
1929New Phytologist XXVIII. 41 These differences may partly be accounted for by the fact that an interval elapses—called by some authors the ‘plastochron’—between the initiation of successive primordia. 1938Priestley & Scott Introd. Bot. xiii. 173 In the 2/5 system it will be noted..that each primordium is three plastochrones removed from its one neighbour, two from the other. 1957Amer. Jrnl. Bot. XLIV. 298/1 A plastochron is conventionally defined as the time interval between initiation of two successive leaves. It might be more broadly defined as the interval between corresponding stages of development of successive leaves, and one might choose initiation, maturity, or any intermediate stage of development as the stage of reference. 1960Ibid. XLVII. 707/1 This plastochron, averaging 3 wk. in length, delimits the 2 developmental stages of the heterophyllous shoot.
b. Special Combs.: plastochron index, an index of the developmental age of a shoot, being the number of leaves that are not less than some stated length, plus a fractional adjustment so calculated that the value of the index changes smoothly as the shoot grows; plastochron ratio (see quot. 1948).
1955F. J. Michelini (title of Ph.D. Dissertation, Univ. Pennsylvania) The use of the plastochron index in studies of morphological and physiological development in Xanthium italicum Moretti. 1973R. Maksymowych Anal. Leaf Development i. 5 The leaf plastochron index (LPI) can be used in developmental studies limited specifically to only one leaf.
1948F. J. Richards in Symp. Soc. Exper. Biol. II. 226 The differences between the various orders of phyllotaxis have been referred to differences in the ratio of the distances of two successive primordia from the apical centre... The ratio will be referred to as the ‘plastochrone ratio’. 1968C. W. Wardlaw Morphogenesis in Plants ix. 231 As the several systems..in Fibonacci phyllotaxis have closely comparable divergence angles, i.e. about 137·5°, the essential differences between them are due to their plastochrone ratios. As the P.R. approaches unity, the phyllotaxis rises.
Hence plastoˈchronic a.
1953K. Esau Plant Anat. v. 104 The changes in the morphology of the shoot apex occurring during one plastochron may be referred to as plastochronic changes. 1957Amer. Jrnl. Bot. XLIV. 302/1 Much would be gained by determining the precise plastochron age of each apex, rather than..judging the plastochronic phase subjectively. |