This study investigated the seasonal modification of wax deposition, and the impact of epicuticular wax on gas-exchange as well as photoinhibition in Leucadendron lanigerum, a species from the Proteaceae family with wax-covered leaf surfaces and the stomata also partially occluded by wax. The results of this study demonstrated that the deposition of epicuticular wax in L. lanigerum is dependent on the age of the leaf as well as the season, and generation and regeneration of wax occur mostly in spring while transformation and also degeneration of wax crystals occur in winter. Epicuticular waxes decreased cuticular water loss, but had little impact on leaf reflectance. The temperature of leaves without wax was lower than that of wax-covered leaves, indicating that the rate of transpiration impacted more on leaf temperature than reflectance of light in the PAR range in L. lanigerum. The wax coverage at the entrance of stomata in L. lanigerum increased resistance to gas diffusion and as a consequence decreased stomatal conductance, transpiration and photosynthesis. Also, the results indicated that epicuticular waxes do help prevent photodamage in L. lanigerum, and so this property could benefit plants living in arid environments with high solar radiation.

The impact of epicuticular wax on gas-exchange and photoinhibition in Leucadendron lanigerum (Proteaceae)

Foliar secretory cavities, commonly called leaf pellucid glands, have been reported in many families of vascular plants. In the Rubiaceae, these structures have only been found in the sister genera Rustia and Tresanthera, which are also anomalous within the family because they have poricidal anthers, and in the distantly related Heterophyllaea. General leaf anatomy, with particular attention to secretory cavities, as well as the chemical analysis of the secreted substances of Rustia formosa, is presented here for the first time. The secretory structures have been found in the lamina between the palisade and spongy parenchymas and in the cortical region of the petiole. The chemical analysis showed that the essential oil secreted is a complex mixture of at least 75 components, mostly of sesquiterpenoid composition. Illustrations of the leaf anatomy, details of the secretory structures of Rustia formosa, a gas chromatogram, and a table of the principal components of the leaf essential oil are included.

https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.2307/3558376

Anatomical and chemical analyses of leaf secretory cavities of Rustia formosa (Rubiaceae)

Notes on the cuticular ultrastructure of six xerophytes from southern Africa

O presente estudo teve como objetivo descrever a anatomia da folha e do caule adulto enfatizando a caracterizacao dos tricomas e das estruturas secretoras do cacaueiro. Foram analisadas amostras de caule e folhas (limbo e peciolo), correspondente ao 3o no, alem de folhas novas de 5cm de comprimento. A lâmina foliar e hipoestomatica, com estomatos do tipo anomocitico. Em ambas as faces do limbo ocorrem quatro tipos de tricomas: sendo dois tectores e dois glandulares. Na epiderme adaxial estao presentes as glândulas secretoras de mucilagem. O mesofilo e dorsiventral; o parenquima palicadico e formado por duas ou tres camadas. O parenquima lacunoso apresenta celulas coletoras. Ao longo do mesofilo predomina feixes colaterais envolvidos por bainha esclerenquimatica que se estende ate as epidermes. O padrao de venacao e do tipo Camptodroma com ramificacoes mistas Brochidrodomas e Eucamptodromos. O peciolo e o caule apresentam a epiderme com os tricomas descritos para o limbo; No parenquima cortical e medular do peciolo e caule, ha celulas contendo graos de amido, idioblastos contendo drusas e canais de mucilagem. O sistema vascular ao longo do peciolo se diferencia quanto a organizacao. O caule apresenta camadas de clorenquima, e de colenquima. Ocorre a esclerificacao das celulas deste ultimo, com o desenvolvimento. Segue-se um anel descontinuo de fibras do floema primario. A medula e ampla e se esclerifica com o desenvolvimento.

CONTRIBUIÇÃO AO ESTUDO ANATÔMICO DA FOLHA E DO CAULE DO CACAUEIRO (Theobroma cacao L.)

Young stem and leaf anatomy of 15 Malagasy-endemic Diospyros species (Ebenaceae): taxonomic implications

An anatomical investigation of the leaves of Antizpma miersiana (Menispermaceae) and Diospyros ramulosa (Ebenaceae), both xerophytic, woody evergreen species, was conducted. Specimens were collected in the arid regions of Namaqualand in southern Africa. A number of classical xeromorphic features are present in A. miersiana, namely thick, cutinized outer epidermal cell walls, a thick epicuticular wax layer, sunken stomata, and mesophyll tissue consisting of a number of palisade parenchyma layers. Two notable features are papillose epidermal cells and large secretory cavities in the mesophyll or associated with the vascular bundles. The leaves of D. ramulosa do not exhibit many features which may be regarded as xeromorphic. An obvious feature of this species is the occurrence of phenolic deposits in the mesophyll and epidermal cells. The leaf anatomy is discussed in relation to its ecological significance.

A. Jordaan

Papers

Structure of xerophytic plants from southern africa. leaf anatomy of antizoma miersiana and diospyros ramulosa