Shoot apex, leaf development and unifacial tip inAgave wightii drumm. et prain (agavaceae)

1984 ◽  
Vol 97 (4) ◽  
pp. 437-446
Author(s):  
Vishnu Kumar ◽  
Devendra K. Awasthi ◽  
Yerramilli S. Murty
Keyword(s):  
Shoot Apex ◽  
Leaf Development

The rotated-lamina syndrome. VII. Direct formation of lamina in the rotated position in Pterospermum (Sterculiaceae) and the appearance of hyper-rotation

1997 ◽  
Vol 75 (1) ◽  
pp. 188-206 ◽  
Author(s):  
W. A. Charlton
Keyword(s):  
Normal Form ◽  
Shoot Apex ◽  
Leaf Development ◽  
Extreme Case ◽  
Lower Side ◽  
Symmetrical Form ◽  
Direct Formation ◽  
Saltational Evolution ◽  
Unidentified Species ◽  
Mode Of Development

The genus Pterospermum presents an extreme case of lamina rotation in their dorsiventral distichous shoots. In Pterospermum suberifolium and an unidentified species, the young laminae emerge from the bud with their upper surfaces facing towards the upper side of the shoot, and, in this, they resemble most other cases of lamina rotation. In Pterospermum heterophyllum and Pterospermum acerifolium, the lamina emerge in hyper-rotated orientation, with the upper surface of the lamina facing outwards away from the parent axis in P. heterophyllum or outwards and towards the lower side of the shoot in P. acerifolium. The early development of the lamina is unusual in all cases, since it appears to arise directly in the rotated position. This unusual mode of lamina development appears to be a case of saltational evolution. In P. acerifolium and P. heterophyllum, the leaf buttress also develops asymmetrically in the manner of other lamina rotators previously described, so that the lamina is rotated further with the formation of a triangular axillary site. This may be a relic of a more "normal" form of lamina rotation. Shoots with spiral phyllotaxis also occur in P. acerifolium, and in P. heterophyllum to a lesser extent, and these shoots have palmately lobed peltate leaves in contrast with the simple leaves of the dorsiventral shoots. The laminae in these shoots arise in a peculiar orientation, so that the upper surface of the lamina faces in the direction of growth of the shoot and never faces towards the shoot apex on which it formed. The mode of early lamina development in the spiral shoots is very similar to that of the dorsiventral shoots, but in the spiral shoots, the lamina is symmetrically placed instead of facing to one side of the shoot. It is suggested that the peculiar orientation of the lamina in the dorsiventral shoots arose first, and then a symmetrical form of this mode of development became incorporated into the leaves of the spiral shoots. Key words: Sterculiaceae, leaf, development, dorsiventrality, lamina rotation, hyper-rotation.

The rotated-lamina syndrome. VI. The range from partial to near-complete rotation in Tiliaceae and Sterculiaceae

1997 ◽  
Vol 75 (1) ◽  
pp. 170-187 ◽  
Author(s):  
W. A. Charlton
Keyword(s):  
Key Words ◽  
Shoot Apex ◽  
Leaf Development ◽  
Leaf Primordia

The rotated-lamina syndrome is a condition most commonly found in dorsiventral shoots with distichous phyllotaxis. Typically, young laminae in bud appear to be rotated to face towards the upper side of the shoot. The syndrome arises by asymmetrical growth from leaf primordia that initially face the shoot apex in approximately the normal way. It was previously described in Tilia. Further genera of Tiliaceae and the closely related Sterculiaceae were examined for the presence of the syndrome. Altogether it was found in 9 genera of the 30 examined. The syndrome is well developed in representatives of Commersonia, Corchorus, and Pterospermum, and less well developed in Luehia seemannii. Expression of the syndrome is minimal in Luehia divaricata, Theobroma, Byttneria, and Grewia. In all cases with distichous phyllotaxis that were examined in these families, the leaf primordia show at least some asymmetry in development and consequently there appears to be a predisposition to lamina rotation within the group. The syndrome is probably becoming suppressed in cases with minimal expression. The situation in dorsiventral shoots of Corchorus and Byttneria is complicated by the presence of inflorescences that arise in a leaf-opposed position. Key words: Sterculiaceae, Tiliaceae, leaf, development, dorsiventrality, lamina rotation.

Molecular genetic approaches to leaf development: Knotted and beyond

1994 ◽  
Vol 72 (5) ◽  
pp. 617-625 ◽  
Author(s):  
Laurie G. Smith ◽  
Sarah Hake
Keyword(s):  
Molecular Genetics ◽  
Shoot Apex ◽  
Leaf Development ◽  
Molecular Basis ◽  
Leaf Surface ◽  
Molecular Genetic ◽  
Leaf Morphogenesis ◽  
Promising Alternative ◽  
Recessive Mutations ◽  
Experimental Approaches

Molecular genetics provides a promising alternative to other experimental approaches for furthering our understanding of the mechanisms controlling leaf development. We investigated the molecular basis of dominant Knotted (Kn1) mutations in maize, which cause cells associated with the lateral veins of the leaf blade to acquire characteristics of sheath or auricle and sporadically form outgrowths called knots. The kn1 gene encodes a homeodomain, a DNA-binding domain shared by many transcription factors that regulate developmental processes in animals and fungi. In normal plants, the expression of kn1 is confined to the shoot apex, but in Kn1 mutants, the gene is also expressed ectopically in the veins of developing leaves, apparently causing cells to change their developmental fates. The kn1 gene may function in the shoot apex of normal plants to promote indeterminate growth. Consistent with this hypothesis, when kn1 is expressed constitutively at high levels in the leaves of transgenic tobacco, shoots are formed on the leaf surface. Thus, our results indicate that while the kn1 gene may normally have no function in leaf development, it can alter the development of maize and tobacco leaves when it is expressed in the leaf inappropriately. Genes that normally play a role in leaf development are more likely to be defined by recessive mutations that alter leaf morphogenesis and histogenesis. Key words: leaf development, molecular genetics, Knotted.

In vitro morphogenesis in Osmunda cinnamomea. The role of the shoot apex in early leaf development

1969 ◽  
Vol 47 (4) ◽  
pp. 575-580 ◽  
Author(s):  
G. S. Hicks ◽  
T. A. Steeves
Keyword(s):  
Shoot Apex ◽  
Leaf Development ◽  
Leaf Primordia ◽  
Shoot Apices ◽  
In Vitro Morphogenesis ◽  
Indeterminate Growth ◽  
Nutrient Culture ◽  
Determinate Growth

In sterile nutrient culture, shoot apices of the rhizome of Osmunda cinnamomea L., devoid of all visible foliar primordia, quickly give rise to dorsiventral leaf primordia at a presumptive leaf site (I1). It was established that these primordia were irreversibly determined as leaves. To examine the morphogenetic role of the shoot apex in governing early leaf development, this site was permanently isolated from the shoot apex by a single tangential cut. Usually, radially symmetrical shoots of indeterminate growth arose at I1 as a result of this surgery. By contrast, when organic continuity between I1 and the shoot apex was only temporarily interrupted by a cut which was subsequently allowed to heal, normally oriented dorsiventral leaf primordia formed most frequently at I1. These, too, were determined as leaves. It was concluded that the shoot apex serves as a source of determinative influences for the nascent primordium, imposing dorsiventrality and a pattern of determinate growth on the leaf site.

The rotated-lamina syndrome. V. Partial lamina rotation and related features in Hamamelidaceae

1994 ◽  
Vol 72 (5) ◽  
pp. 626-634 ◽  
Author(s):  
W. A. Charlton
Keyword(s):  
Key Words ◽  
Shoot Apex ◽  
Leaf Development ◽  
Early Stage ◽  
Leaf Primordia ◽  
Leaf Base ◽  
Early Stages ◽  
Young Leaves

Shoots of Hamamelidaceae have been examined for the presence of the rotated-lamina syndrome, a condition in which young leaves in bud face towards one side of the shoot (normally the upper) rather than towards their own shoot apex. Early leaf development and bud organisation have been examined in representatives of eight genera with dorsiventral shoots and distichous phyllotaxis, and of four genera with radially symmetrical shoots and spiral or decussate phyllotaxis. Radially symmetrical shoots do not show any evidence of the syndrome. The distichous Corylopsis and Hamamelis species studied have leaf primordia that are asymmetrical from an early stage and show partial lamina rotation, the lamina facing obliquely towards the upper side of the bud. Mature laminae are usually asymmetrical. In Corylopsis rotation arises by torsion in the petiole region, and in Hamamelis by asymmetrical growth of the leaf base. Distichous examples without lamina rotation also have asymmetrical primordia in most cases, often have asymmetrical leaves, and all show the same asymmetrical development of the leaf base as found in Hamamelis. It is suggested that these features represent either (i) relics of rotated-lamina syndrome that was present in these cases but has been suppressed or (ii) early stages in evolution of rotated-lamina syndrome. It is suggested that suppression is the more likely interpretation. Corylopsis and Hamamelis may also be in the process of suppressing the syndrome. Key words: Hamamelidaceae, leaf, development, dorsiventrality, lamina rotation.

The rotated-lamina syndrome. IV. Relationships between rotation and symmetry in Magnolia and other cases

1994 ◽  
Vol 72 (1) ◽  
pp. 25-38 ◽  
Author(s):  
W. A. Charlton
Keyword(s):  
Key Words ◽  
Shoot Apex ◽  
Leaf Development ◽  
Leaf Primordia ◽  
The State ◽  
Axillary Buds ◽  
Reverse Direction ◽  
Ulmus Glabra ◽  
Young Leaves

Further variations of the rotated-lamina syndrome are described in Magnolia spp. and Rhamnus imeretinus, as well as an abnormal adult shoot of Ulmus glabra without lamina rotation. All magnolias investigated show lamina rotation, but there are four possible forms of shoot symmetry: (i) dorsiventral distichous shoots with the form of rotated-lamina syndrome previously described, i.e., laminae of young leaves all face towards the same (upper) side of the bud or towards the parental axis in axillary buds; (ii) another form of dorsiventral symmetry in which lamina rotation occurs in the reverse direction; (iii) spiral phyllotaxis with laminae rotated to face up the genetic spiral; and (iv) spiral phyllotaxis with laminae rotated to face down the genetic spiral. Shoot symmetry and development of lamina rotation in leaf primordia correlate with the taxo-nomic subdivision of the genus. Shoots of R. imeretinus are dorsiventral, with leaves arranged in four ranks, and lamina rotation occurs towards the upper side of the shoot. The sense of rotation of leaf primordia reverses with a periodicity of two plastochrons. In the abnormal shoot of Ulmus without lamina rotation, phyllotaxis was distichous and leaf primordia were symmetrical. The various cases are discussed in relation to the previously erected hypothesis that control of development in dorsiventral shoots with the rotated-lamina syndrome resides in alternating states of asymmetry in the shoot apex, and the corollary that a shoot with spiral phyllotaxis and one sense of lamina rotation should result if the state of asymmetry is maintained and does not alternate. Key words: Magnolia spp., Rhamnus imeretinus, Ulmus glabra, leaf, development, dorsiventrality, lamina rotation.

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