Difference in cuticular transpiration and sclerophylly in juvenile and adult pine needles relates to the species-specific rates of development

Pinus species show remarkable ontogenetic differences in needle morphology (heterophylly) between juvenile and adult vegetative phases. This developmental shift may play an adaptative role in their success under diverse habitats. As a first step to know the functional differences between each vegetative phase, we compared water loss through the cuticles of juvenile and adult needles of 21-month-old nursery-grown seedlings of nine hard pine species. Cuticular transpiration (CT), calculated after complete stomatal closure, was obtained by leaf-drying curves, and was related to leaf, ontogenetic and climatic parameters. The rate of cuticular transpiration (RCT) between juvenile and adult needles differed across pine species, and in particular segregated the Mediterranean species Pinus canariensis and P. halepensis, from the Eurasian P. uncinata and introduced species P. radiata. For these species, RCT was always higher in juvenile needles. The different leaf and ontogenic parameters studied were correlated with the variation in RCT among the nine pine species. We discuss this relationship in the light of the species ecology. Besides their possible adaptive interpretation, these results suggest an underlying need to consider the ontogenetic heterophylly when assessing functional traits in hard pine seedlings, in particular those traits that govern water relations.     

Effects of ethylene and abscisic acid upon heterophylly in<Emphasis Type="Italic"> Ludwigia arcuata</Emphasis> (Onagraceae)

In this study, we examined the effects of ethylene and abscisic acid (ABA) upon heterophyllous leaf formation of Ludwigia arcuata Walt. Treatment with ethylene gas resulted in the formation of submerged-type leaves on terrestrial shoots of L. arcuata, while treatments with ABA induced the formation of terrestrial-type leaves on submerged shoots. Measurement of the endogenous ethylene concentration of submerged shoots showed that it was higher than that of terrestrial ones. In contrast, the endogenous ABA concentration of terrestrial shoots was higher than that of submerged ones. To clarify interactions of ethylene and ABA, simultaneous additions of these two plant hormones were examined. When L. arcuata plants were treated with these two plant hormones, the effects of ABA dominated that of ethylene, resulting in the formation of terrestrial-type leaves. This suggests that ABA may be located downstream of ethylene in signal transduction chains for forming heterophyllous changes. Further, ethylene treatment induced the reduction of endogenous levels of ABA in tissues of L. arcuata, resulting in the formation of submerged-type leaves. Thus the effects of ethylene and ABA upon heterophyllous leaf formation are discussed in relationship to the cross-talk between signaling pathways of ethylene and ABA.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - L/W ratio ratio of leaf length to width - LN leaf number - GAs gibberellins     

Cellular basis of developmental plasticity observed in heterophyllous leaf formation of Ludwigia arcuata (Onagraceae)

When heterophyllous plants of Ludwigia arcuata Walt. (Onagraceae) were transferred from aerial condition to submergence, young developing leaves were matured into leaves with intermediate shape between aerial-type and submerged-type, showing spatulate shape (spoon-shaped). This change was also induced by the exposure of plants to ethylene. On the other hand, when the plants were transferred from submergence to aerial conditions, young developing leaves were matured into intermediate-type leaves with elliptic shape (spearhead shape). Anatomical analysis revealed that the formation of spatulate leaf was caused by the reduction of the number of epidermal cells aligned in the leaf transverse direction in the basal region of the leaf while the tip regions remained as before and did not respond to this treatment. During development, the ethylene-induced spatulate leaves showed that three types of alterations in epidermal cell division were involved in this process. Changes in the distribution of cell divisions in leaf lamina were detected by the first day of ethylene exposure, and changes in the orientation of cell division planes were detected by the second day. However, changes in the number of cells aligned in the leaf transverse direction were not detected by this time. Three days after ethylene exposure, frequency of cell divisions changed, and by the time changes of cell numbers aligned in the leaf transverse direction were observed. Thus, the formation of intermediate-type leaves in L. arcuata was ascribed to the alterations of cell division patterns which was induced by ethylene.     

Leaf life span of floating-leaved plants

Photosynthetic capacity of floating-leaved plants is relatively high comparable with terrestrial herbaceous plants, though floating-leaved plants have a much smaller biomass with a leaf area index seldom exceeding 2m²m^-2. Their rather small biomass accumulation is related to higher turnover of leaf biomass or shorter leaf life span. Life span of floating leaves reported in the literature ranged mostly from 13 to 35 days, shorter than that of any other groups of herbaceous macrophytes. Floating-leaved plants are known to show considerably high plasticity in their leaf form. Leaf life span could be prolonged for Nymphoides peltata (Gmel.) O. Kuntze grown in a terrestrial environment and for emergent leaves of Nelumbo nucifera Gaertn. Their short leaf life span seems to be closely related to the fact that old leaves covered by newly formed ones are inevitably compelled to be submerged and lose their function as a photosynthetic apparatus.Abbreviations LAI leaf area index - PFD photosynthetic photon flux density     

Temperature-dependent changes of cell shape during heterophyllous leaf formation in <Emphasis Type="Italic">Ludwigia </Emphasis><Emphasis Type="Italic">arcuata</Emphasis> (Onagraceae)

Although elongation of epidermal cells in submerged leaves is thought to be a common feature of heterophyllous aquatic plants, such elongation has not been observed in Ludwigia arcuata Walt. (Onagraceae). In this study we found that reduced culture temperature induced the elongation of epidermal cells of submerged leaves in L. arcuata. Since such submerged leaves also showed a reduction in the number of epidermal cells aligned across the leaf transverse axis, these data indicate that heterophyllous leaf formation in L. arcuata is partially temperature sensitive, i.e., the elongation of epidermal cells was temperature sensitive while the reduction in the number of epidermal cells did not show such temperature sensitivity. To clarify the mechanisms that cause such temperature sensitivity, we examined the effects of ethylene, which induced the formation of submerged-type leaves on aerial shoots at the relatively high culture-temperature of 28 degrees C. At 23 degrees C, ethylene induced both cell elongation and reduction in the number of epidermal cells across the leaf transverse axis, while cell elongation was not observed at 28 degrees C. Moreover, both submergence and ethylene treatment induced a change in the arrangement of cortical microtubules (MTs) in epidermal cells of developing leaves at 23 degrees C. Such changes in the arrangement of MTs was not induced at 28 degrees C. Factors involved in the temperature-sensitive response to ethylene would be critical for temperature-sensitive heterophyllous leaf formation in L. arcuata.     

Inherited maternal effects on the drought tolerance of a natural hybrid aquatic plant, <Emphasis Type="Italic">Potamogeton anguillanus</Emphasis>

We tested whether maternal effects have led to the adaptive divergence of strains of the natural hybrid Potamogeton anguillanus, whose putative parents show contrastingly divergent ecologies. To examine the correlation between phenotypic characters and maternal types, we conducted drought experiments and DNA typing using nuclear and chloroplast genes. In the field, we investigated the distribution of the maternal type along the depth and the inshore-offshore gradient. Hybrids of P. malaianus mothers (M-hybrids) and those of P. perfoliatus mothers (P-hybrids) could not be distinguished morphologically under submerged conditions, but differed in drought tolerance. M-hybrids and P. malaianus formed more terrestrial shoots and exhibited higher survival than P-hybrids and P. perfoliatus in drought experiments. The distribution survey clarified that M-hybrids were dominant in shallow and inshore areas, whereas they were almost absent in deeper and offshore areas. These results indicate that the natural hybrid P. anguillanus differs in adaptive values depending on the maternal type. Bidirectional hybridization and heritable maternal effects may have played important roles in its phenotypic adaptation to local environmental conditions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Heterophylly results in a variety of “spectral signatures” in aquatic plant species

The leaf reflectance spectra (280–887 nm) of two heterophyllous aquatic plant species Polygonum amphibium (L.) and Nuphar luteum (L.) were compared and their relation to physical properties of the leaves examined. In P. amphibium contrasting environmental conditions along water–land gradient affected the majority of anatomical and morphological properties of leaves, but less differences were observed in photosynthetic pigment and total flavonoid contents. Leaf mass per area (LMA), palisade mesophyll, leaf thickness, trichome length and anthocyanin content per dry mass were correlated to the different parts of spectra. In N. luteum natant and submerged leaves differed significantly in all measured parameters. Chlorophyll a, anthocyanin and carotenoid contents per dry mass were related to reflectance in the red region, while leaf thickness, anthocyanin and total flavonoid contents per leaf area were related to reflectance in the near infrared region. Redundancy Analysis (RDA) indicated that in P. amphibium the average length of trichomes and LMA explained 72% and 6% variability of the spectra, whereas in N. luteum anthocyanin content per dry mass, explained 57% variability of the spectra. The comparison of natant leaves of both species showed that they were more similar than different leaf types within the single species.     

Physiological consequences of changes in life form of the Mexican epiphyte Tillandsia deppeana (Bromeliaceae)

Summary The heterophyllous epiphyte Tillandsia deppeana exhibits an atmospheric habit as a juvenile and a tank form as an adult. Both juveniles and adults utilize C₃ photosynthesis. This is the first report of an atmospheric form of Tillandsia which does not exhibit CAM. Photosynthetic saturation occurred at approximately 10% of full sunlight in both forms, but the adults exhibited greater rates of photosynthesis at all levels of irradiance. The adults also had a higher and broader photosynthetic temperature optimum than did the juveniles. The adults transpired at greater rates than the juveniles; however, the water use efficiencies of both forms were similar and were high for C₃ plants. In both forms the photosynthetic rate decreased in response to a decrease in humidity. After 8 days without water the juveniles were able to fix CO₂ throughout the day. The adults, however, exhibited a net loss of CO₂ on the second day without water and thereafter. These results indicate that the water-conservative atmospheric juvenile of T. deppeana is well adapted to establishment in the epiphytic habitat.