Developmental and ultrastructural characters of the pollen grains and tapetum in species of Nymphaea subgenus Hydrocallis

GALATI, B. G.; ZINI, L. M.; FERRUCCI, M. S.; ZARLAVSKY, G.

PROTOPLASMA

SPRINGER WIEN

Lugar: Viena; Año: 2017

0033-183X

Variations in pollen characters and tapetum behaviorwere recently acknowledged in the early-divergent familyNymphaeaceae and even within the genus Nymphaea, whichprobably is not monophyletic; some traits such as infratectumand tapetum type are also a matter of different interpretations.In this study, developmental characters of the pollen grainsand tapetum in Nymphaea subgenus Hydrocallis are providedfor the first time. Observations were made in N. amazonum,N. gardneriana, and N. prolifera using light, scanning, andtransmission electron microscopy. Tapetum is of the secretorytype and produces orbicules. At microspore and pollen grainstages, the distal and proximal walls differ considerably. Thisresult supports the operculate condition of the aperture inHydrocallis, and such aperture might be plesiomorphic forNymphaeoideae. The infratectum is intermediate, composedof inter-columellae granular elements, robust columellaeconsisting of agglomerated granules, complete columellae,and fused columellae. Narrow microchannels are present andpersist until the mature pollen grain stage. The membranousgranular layer is often present in the pollen grains ofNymphaeaceae. In N. gardneriana, this layer is most probablya component of the intine because it is lost after acetolysis.Orbicules in the Nymphaeaceae are characterized as sphericalor subspherical, with a smooth sporopolleninic wall that surroundsan electron-lucent core and with individual orbiculesthat usually merge to give irregular aggregations. The aperture,pollen wall ultrastructure, and the tapetum of the studiedspecies are discussed in an evolutionary and systematic context,and these characters are also compared with those ofother angiosperm lineages.