Anisocotyly and meristem initiation in an unorthodox plant, Streptocarpus rexii (Gesneriaceae).
In common with most Old World Gesneriaceae; Streptocarpus Lindl. shows anisocotylous growth, i.e., the continuous growth of one cotyledon after germination. Linked to this phenomenon is an unorthodox behaviour of the shoot apical meristem (SAM) that determines the growth pattern of acaulescent species (subgenus Streptocarpus). In contrast caulescent species develop a conventional central post-embryonic SAM (mainly subgenus Streptocarpella). We used S. rexii Lindl. as a model to investigate anisocotyly and meristem initiation in Streptocarpus by using histological techniques and analyses of the expression pattern of the meristematic marker SrSTM1 during ontogeny. In contrast to Arabidopsis thaliana (L.) Heynh., S. rexii does not establish a SAM during embryogenesis, and the first evidence of a SAM-like structure occurs during post-embryonic development on the axis (the petiolode) between the two cotyledons. The expression pattern of SrSTM1 suggests a function in maintaining cell division activity in the cotyledons before becoming localized in the basal meristem, initially at the proximal ends of both cotyledons, later at the base of the continuously growing macrocotyledon, and the groove meristem on the petiolode. The latter is equivalent to a displaced SAM seemingly originating de novo under the influence of endogenous factors. Applied cytokinin retains SrSTM1expression in the small cotyledon, thus promoting isocotyly and re-establishment of a central post-embryonic SAM. Hormone-dependent delocalization of the process of meristem development could underlie anisocotyly and the unorthodox SAM formation in Streptocarpus.
Mantegazza
Raffaella
R
Dipartimento di Biologia, Universita degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy. raffaella.mantegazza@unimi.it
Möller
Michael
M
Harrison
C Jill
CJ
Fior
Simone
S
De Luca
Chiara
C
Spada
Alberto
A
D018548:Cotyledon / Q000196:embryology / Q000235:genetics* / Q000648:ultrastructure; D003583:Cytokinins / Q000494:pharmacology; D029624:Ferns / Q000196:embryology / Q000235:genetics*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017403:In Situ Hybridization; D018519:Meristem / Q000196:embryology / Q000235:genetics* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics
D003583:Cytokinins; D010937:Plant Growth Regulators; D010940:Plant Proteins