Crassula, insights into an old, arid-adapted group of southern African leaf-succulents.

The Crassulaceae is an important family in the Greater Cape Floristic Region of southern Africa and is the seventh largest family in the arid Succulent Karoo Biome. After the Aizoaceae it is the largest group of leaf-succulents in southern Africa. This is the first investigation of a broad selection (68%) of the ±170 species of Crassula. We used data from three chloroplast and two nuclear gene-regions, which yielded many informative characters and provided good resolution among the species. We show that only five of the 20 sections in Crassula are monophyletic. However, the clades recovered show close correlation with the two subgenera that were once recognized. Crassula contains more than 25 succulent annual species which are not closely related to each other but form early-diverging branches in each of the three major clades. One of these major clades contains far more perennial species than the others and is the greatest diversification within Crassula. This diversification mostly arose within the last 10 million years (my) and spread across much of southern Africa. Members of the smaller two major clades are often soft- and flat-leaved perennials (many with basic chromosome number x = 8, with high levels of polyploidy). Those in the largest diversification (where a basic chromosome number of x = 7 predominates) show other arid-adaptations (more highly succulent leaves with a dense covering of hairs or papillae or a smooth xeromorphic epidermis). Their flowers are also more variable in shape and bee-, moth- and butterfly-pollinated species are known among them. We establish that Crassula arose in the Greater Cape Floristic Region of southern Africa. While much of its diversity has evolved in the last 10 my, Crassula nevertheless contains species that are much older and itself arose ±46 my ago. Since all its species are succulent it is possible that they are part of an early arid-adapted flora that contributed to the Succulent Karoo Biome in the western part of southern Africa. Consequently this Biome may not be assembled only from 'young lineages' as is usually thought to be the case.

Facultative CAM photosynthesis (crassulacean acid metabolism) in four species of Calandrinia, ephemeral succulents of arid Australia.

Crassulacean acid metabolism (CAM) was demonstrated in four small endemic Australian terrestrial succulents from the genus Calandrinia (Montiaceae) viz. C. creethiae, C. pentavalvis, C. quadrivalvis and C. reticulata. CAM was substantiated by measurements of CO2 gas-exchange and nocturnal acidification. In all species, the expression of CAM was overwhelmingly facultative in that nocturnal H+ accumulation was greatest in droughted plants and zero, or close to zero, in plants that were well-watered, including plants that had been droughted and were subsequently rewatered, i.e. the inducible component was proven to be reversible. Gas-exchange measurements complemented the determinations of acidity. In all species, net CO2 uptake was restricted to the light in well-watered plants, and cessation of watering was followed by a progressive reduction of CO2 uptake in the light and a reduction in nocturnal CO2 efflux. In C. creethiae, C. pentavalvis and C. reticulata net CO2 assimilation was eventually observed in the dark, whereas in C. quadrivalvis nocturnal CO2 exchange approached the compensation point but did not transition to net CO2 gain. Following rewatering, all species returned to their original well-watered CO2 exchange pattern of net CO2 uptake restricted solely to the light. In addition to facultative CAM, C. quadrivalvis and C. reticulata exhibited an extremely small constitutive CAM component as demonstrated by the nocturnal accumulation in well-watered plants of small amounts of acidity and by the curved pattern of the nocturnal course of CO2 efflux. It is suggested that low-level CAM and facultative CAM are more common within the Australian succulent flora, and perhaps the world succulent flora, than has been previously assumed.

[Induction on callus culture and regeneration of Orostachyis fimbriatae].

OBJECTIVE: To explore the effects of different hormonal combinations on induction, proliferation and differentiation of Orostachyis fimbriatae callus culture. METHODS: Aseptic seedling leaves were used as explants,the different concentrations of IAA,NAA, 6-BA and KT on induction proliferation of callus were optimized by orthogonal test to explore the optimum medium for differentiation of callus by tissue culture techniques. RESULTS: The best medium for induction was MS + IAA 1.0 mg/L + NAA 0.5 mg/L + KT 1.0 mg/L, and the best hormonal combination for proliferation was MS + IAA 0.5 mg/L + 6-BA 0.5 mg/I. + KT 1.0 mg/L. The best medium for differentiation was MS + IAA 0.1 mg/L + KT 2.0 mg/L, and 1/2MS + IAA 0.2 mg/L was the optimum medium for rooting culture. CONCLUSION: The system of regeneration of Orostachyis fimbriatae is establishd by tissue culture techniques in this study.

How succulent leaves of Aizoaceae avoid mesophyll conductance limitations of photosynthesis and survive drought.

In several taxa, increasing leaf succulence has been associated with decreasing mesophyll conductance (g M) and an increasing dependence on Crassulacean acid metabolism (CAM). However, in succulent Aizoaceae, the photosynthetic tissues are adjacent to the leaf surfaces with an internal achlorophyllous hydrenchyma. It was hypothesized that this arrangement increases g M, obviating a strong dependence on CAM, while the hydrenchyma stores water and nutrients, both of which would only be sporadically available in highly episodic environments. These predictions were tested with species from the Aizoaceae with a 5-fold variation in leaf succulence. It was shown that g M values, derived from the response of photosynthesis to intercellular CO2 concentration (A:C i), were independent of succulence, and that foliar photosynthate δ(13)C values were typical of C3, but not CAM photosynthesis. Under water stress, the degree of leaf succulence was positively correlated with an increasing ability to buffer photosynthetic capacity over several hours and to maintain light reaction integrity over several days. This was associated with decreased rates of water loss, rather than tolerance of lower leaf water contents. Additionally, the hydrenchyma contained ~26% of the leaf nitrogen content, possibly providing a nutrient reservoir. Thus the intermittent use of C3 photosynthesis interspersed with periods of no positive carbon assimilation is an alternative strategy to CAM for succulent taxa (Crassulaceae and Aizoaceae) which occur sympatrically in the Cape Floristic Region of South Africa.

Rarity as a life-history correlate in Dudleya (Crassulaceae).

PREMISE OF THE STUDY: Differences in rarity among species can be caused by adaptation to local conditions along with correlated evolution in characters that limit geographic range size. For this kind of divergence, the resulting species differ in their ability to thrive in varying environments. Because rare species are more prone to extinction than widespread species, trade-offs in life history predispose the resulting lineages to clade selection. METHODS: Nine Dudleya species live in the Santa Monica Mountains: five neoendemics, one species intermediate in rarity, and three with broader ranges. Life-history traits were correlated against one another. To understand habitat dependence, the species were grown in an inland garden and in a coastal garden, and the disparity in growth and reproduction in the two gardens was compared among species. KEY RESULTS: Rare species reproduced earlier and grew to be smaller than common species. The small body size of the rare species was correlated with small reproductive outputs compared with those of the large-bodied common species. The growth disparity between plants in the two gardens was greatest for the rare species. The rare species had a lower tolerance for hot, dry conditions compared with the common species. In the Santa Monica Mountains, the habitat conditions required by the rare species are not as prevalent as those of the common species. CONCLUSIONS: The data are consistent with the view that differences in life histories constrained by trade-offs affect range size. Such differences in rarity become the grist for clade selection at the scale of macroevolution.

The intramolecular ¹³C-distribution in ethanol reveals the influence of the CO2 -fixation pathway and environmental conditions on the site-specific ¹³C variation in glucose.

Efforts to understand the cause of ¹²C versus ¹³C isotope fractionation in plants during photosynthesis and post-photosynthetic metabolism are frustrated by the lack of data on the intramolecular ¹³C-distribution in metabolites and its variation with environmental conditions. We have exploited isotopic carbon-13 nuclear magnetic resonance (¹³C NMR) spectrometry to measure the positional isotope composition (δ¹³C(i) , ‰) in ethanol samples from different origins: European wines, liquors and sugars from C3, C4 and crassulacean acid metabolism (CAM) plants. In C3-ethanol samples, the methylene group was always ¹³C-enriched (∼2‰) relative to the methyl group. In wines, this pattern was correlated with both air temperature and δ(18)O of wine water, indicating that water vapour deficit may be a critical defining factor. Furthermore, in C4-ethanol, the reverse relationship was observed (methylene-C relatively ¹³C-depleted), supporting the concept that photorespiration is the key metabolic process leading to the ¹³C distribution in C3-ethanol. By contrast, in CAM-ethanol, the isotopic pattern was similar to but stronger than C3-ethanol, with a relative ¹³C-enrichment in the methylene-C of up to 13‰. Plausible causes of this ¹³C-pattern are briefly discussed. As the intramolecular δ¹³C(i) -values in ethanol reflect that in source glucose, our data point out the crucial impact on the ratio of metabolic pathways sustaining glucose synthesis.

[Tissue culture and regeneration of Sedum hybridum].

The cotyledons and hypecotyl of Sedum hybridum were used as explant to induce calluse on MS media supplemented with different concentration of hormone. There were formed two kind of calluses, one was red while other was green. The cotyledon was the ideal explant for the callus induction, its induction rate could be reached 80% - 82% either on MS medium with 6-BA 1 mg/L and 2,4-D 0.5 mg/L or with 6-BA 1 mg/L and NAA 0.5 mg/L. Numerous adventitious buds could formed from calluses on the MS medium with 6-BA 2 mg/L and NAA 0.5 mg/L. The medium for the root growth was 1/2 MS. The tube seedling which can be successfully transplanted at 80% survival.

Clumping and dispersal of chloroplasts in succulent plants.

Plants have evolved various photoprotective mechanisms to mitigate photodamage. Here we report the diurnal movement of chloroplasts in the leaves of succulent crassulacean acid metabolism (CAM) plants under combined light and water stress. In leaves of water-stressed plants, the chloroplasts became densely clumped in one or sometimes two areas in the cytoplasm under light and dispersed during darkness. The chloroplast clumping resulted in leaf optical changes, with a decrease in absorptance and an increase in transmittance. The plant stress hormone abscisic acid induced chloroplast clumping in the leaf cells under light. We suggest that the marked chloroplast movement in these CAM plants is a photoprotective strategy used by the plants subjected to severe water stress.

Movement of water from old to young leaves in three species of succulents.

A hypothetical adaptive response of succulent plants to drought-stress is the redistribution of water from old to young leaves. We examined the effects of possible movement of water from old to young leaves in three succulent species, Carpobrotus edulis (weak CAM-inducible), Kalanchoe tubiflora (CAM) and Sedum spectabile (possibly a CAM-cycler or CAM-inducible). Old leaves were removed from plants, and photosynthesis, transpiration, f. wt : d. wt ratios, diurnal acid fluctuations, stomatal conductance and internal CO2 concentrations of the remaining young leaves were measured during drought-stress. Comparison was made with plants retaining old leaves. There was no evidence that water moved from old to young leaves during drought-stress as previously hypothesized. Only in drought-stressed plants of K. tubiflora, were photosynthetic and transpiration rates of young leaves greater on shoots with old leaves removed compared with attached. There was a trend in all species for greater fluctuations in acidity in young leaves on shoots that lacked older leaves. For two of the three species studied, the f. wt : d. wt ratios of young leaves were greater under drought-stress, on shoots with old leaves removed than with them attached. Absence of old leaves may reduce competition for water with young leaves, which consequently have higher water content and greater photosynthetic rates.