Potential carbon gain of shingle leaves in juveniles of the vine Monstera tenuis (Araceae) in Costa Rica

The amount of light intercepted by vertically oriented, shingle leaves of juvenile Monstera tenuis vines growing in forest understory was compared to the amount of light the leaves would intercept if they were horizontal. Light levels were monitored using quantum sensors and hemispherical photography. Shingle leaves absorb less light than they would if the leaves were horizontal at the same positions, and the difference increases with height in the forest. Modeling based on measured photosynthetic light responses and light interception suggests that at 1 m height, 75% more carbon could be gained if leaves were horizontal instead of vertical. Because the vertical leaf orientation reduces light interception, other selective factors are likely of greater importance in favoring the evolution of the shingle-leaved growth form.     

Rhythmic plant morphogenesis: Recurrent patterns of idioblast cell production

Most plants are constructed from repeating modular units such as phytomers, merophytes, and cell packets. Even an organism as simple as the filamentous cyanobacterium Anabaena shows recurrent patterns of differentiated cellular structures, notably with respect to its heterocysts. These examples reflect the inherent rhythms established within developmental processes of living organisms. In the present article, attention is paid to repetitious production of idioblasts—isolated cells, or clusters of cells, with an identity different to that of neighbouring cells from which they are derived. In higher plant root tissues, idioblasts are contained within cell packets that grow up from mother cells during the course of a number of cycles of cell production. The heterocysts of Anabaena are also discussed; they, too, are a type of idioblast. The idioblasts of root tissues originate as small cells which result from unequal cell divisions. Such divisions are usually the final ones within a cell packet which has already undergone a number of division cycles and are characteristically located at one or both ends of a packet. The packet end walls are suggested to have a role in regulating division asymmetry. Idioblastic systems discussed are root cortical trichosclereids and diaphragm cells; in their earliest stage, the cells from which lateral root primordia arise are also considered as clusters of idioblasts because they, too, are the products of asymmetric divisions of pericyclic mother cells. The division patterns of all these idioblastic systems were modelled in a consistent way using L-systems, with the assumption that the age of a cell-packet end wall plays a special role in cell determination. This article is dedicated to Vsevelod Ya. Brodsky, doyen of Russian studies of rhythms in cell division and development, who celebrates his 80th birthday on August 4, 2008 This article was presented in original.     

Alternative modes of leaf dissection in monocotyledons

Although a majority of monocotyledons have simple leaves, pinnately or palmately dissected blades are found in four orders, the Alismatales, Pandanales, Dioscoreales and Arecales. Independent evolutionary origins of leaf dissection are indicated by phylogenetic analyses and are reflected in the diversity of mechanisms employed during leaf development. The mechanism of blastozone fractionation through localized enhancement and suppression of growth of the free margin of the leaf primordium occurs in the Araceae and Dioscoreaceae. By contrast, the corrugated, dissected leaves of palms (Arecaceae) develop through a two-step process: first, plications are formed through intercalary growth in a submarginal position and, second, the initially simple leaf blade is dissected through an abscission-like process of leaflet separation. A third mechanism, perforation formation, is employed in Monstera and five related genera of the Araceae. In this mode, discrete patches of cells undergo programmed cell death during lamina development, resulting in formation of open perforations. When perforations are positioned near the leaf margin, mechanical disruption of the thin bridges of marginal tissue results in a deeply pinnatisect blade. Whereas blastozone fractionation defines the early primary morphogenesis phase of leaf development, the other two modes occur later, during the secondary morphogenesis/histogenesis phase. Evolution of these mechanisms presumably has involved recruitment of other developmental programmes into the development of dissected leaves.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 25–44.     

Hydraulic architecture of Monstera acuminata: evolutionary consequences of the hemiepiphytic growth form

The hydraulic architecture of the secondary hemiepiphyte Monstera acuminata was examined in native plants from Los Tuxtlas, Veracruz, Mexico, to determine how it compared to better-known growth forms such as trees, shrubs, lianas and primary hemiepiphytes. Monstera acuminata starts its life cycle as a prostrate herb. As it ascends a tree or other vertical support, the stem becomes thicker, produces larger leaves, and may die back from the base upwards until only aerial feeding roots serve to connect the stem to the soil. Unlike the pattern of vessel-size distribution along the stems of woody dicotyledons, M. acuminata has its wider vessels at the top of the stem, decreasing in diameter towards the base. Also peculiar is the fact that Huber values (axis area/distal leaf area) tend to increase exponentially at higher positions within the plant. Based on the hydraulic conductivity ( k _h) and leaf-specific conductivity (LSC, k _h/distal leaf area), the base of the stem potentially acts as a severe hydraulic constriction. This constriction is apparently not limiting, as aerial roots are produced further up the stem. The plants have remarkably strong root pressures, up to 225 kPa, which may contribute to the maintenance of functional vessels by refilling them at night or during periods of very high atmospheric humidity, as in foggy weather and rain. In common with dicotyledonous plants, vessel length, vessel diameter, k _h, specific conductivity ( k _s, k _h/axis area) and LSCs were all positively correlated with axis diameter. The features of the hydraulic architecture of M. acuminata may be an evolutionary consequence of an anatomical constraint (lack of vascular cambium and therefore of secondary growth) and the special requirements of the hemiepiphytic growth form.     

Histochemical localization of nucleoside triphosphatase activity in assimilate conducting plant tissue

Summary For the histochemical localization of nucleoside triphosphatases at the electron microscopic level, prefixed tissues were incubated with lead nitrate in addition to substrate (GOMORI reaction). While ATP and UTP as substrates gave electron-dense reaction products at the plasmalemma of sieve tubes, companion cells and phloem parenchyma cells, and at plasmodesmata in primary pitfields, AMP gave reaction products only at the tonoplast of parenchyma cells. Since electron-dense deposits also occur in cell walls and vacuoles, energy dispersive X-ray microanalysis was used to distinguish between lead deposits and lead-phosphate deposits. The latter were restricted to the symplast. Among the three plant species used, the leaf bundle phloem ofHordeum distichon showed ATPase activity largely restricted to the phloem cells, except for the thickwalled sieve tubes. Some activity also bordered the chloroplasts of the bundle sheath cells. In the C₄ plantGomphrena globosa, ATPase and UTPase activities appeared to be the greater in phloem parenchyma cells than in sieve tubes. In the phloem of youngMonstera deliciosa roots, ATPase occurred not only at the plasmalemma of sieve tubes, but also around sieve-tube plastids. When compared with AMP as substrate, it appears that nucleoside triphosphates are the natural substrates of the enzyme(s) in the plasmalemma of sieve tubes and phloem parenchyma cells.     

A preliminary study of genetic variation in populations of Monstera adansonii var. klotzschiana (Araceae) from North-East Brazil, estimated with AFLP molecular markers

BACKGROUND AND AIMS: This study sought genetic evidence of long-term isolation in populations of Monstera adansonii var. klotzschiana (Araceae), a herbaceous, probably outbreeding, humid forest hemi-epiphyte, in the brejo forests of Ceará (north-east Brazil), and clarification of their relationships with populations in Amazonia and the Atlantic forest of Brazil. METHODS: Within-population genetic diversity and between-population dissimilarity were estimated using AFLP molecular markers in 75 individuals from eight populations located in Ceará, the Brazilian Atlantic Forest and Amazonia. KEY RESULTS: The populations showed a clinal pattern of weak genetic differentiation over a large geographical region (F(ST) = 0.1896). A strong correlation between genetic and geographical distance (Mantel test: r = 0.6903, P = 0.002) suggests a historical pattern of isolation by distance. Genetic structure analysis revealed at least two distinct gene pools in the data. The two isolated Ceará populations are significantly different from each other (pairwise Phi(PT) = 0.137, P = 0.003) and as diverse (Nei's gene diversity, average H(e) = 0.1832, 0.1706) as those in the Atlantic and Amazon forest regions. The population in southern Brazil is less diverse (Nei's gene diversity, average H(e) = 0.127) than the rest. The Ceará populations are related to those of the Atlantic forest rather than those from Amazonia (AMOVA, among-groups variation = 11.95 %, P = 0.037). CONCLUSIONS: The gene pools detected within an overall pattern of clinal variation suggest distinct episodes of gene flow, possibly correlated with past humid forest expansions. The Ceará populations show no evidence of erosion of genetic diversity, although this was expected because of their isolation. Their genetic differentiation and relatively high diversity reinforce the importance of conserving the endangered brejo forests.