Protea Neriifolia Research Articles

Plant Species Complementarity in Low-Fertility Degraded Soil.

The aim of this study was to investigate the compatibility of plants with contrasting root systems, in terms of procurement of limiting soil nutrients. Paired combinations of species of proteas and grasses were grown in a pot experiment using soil from a site with impoverished vegetation and degraded soil. The soil contained sufficient N but was low to deficient in P, Mn, S, Fe, and B. The uptake of chemical elements into the foliage differed significantly according to whether the plants were growing as single or mixed species. When two species of Grevillea and grasses with evolutionary origins in low fertility soils were growing together, there was an enhanced uptake of P and Mn, in one or both species, in addition to other elements that were in low concentrations in the experimental soil. In contrast to this, Protea neriifolia that probably originated from a more fertile soil procured lesser amounts of the six elements from the soil when growing together with grasses. Two grasses tolerant of less fertile soils (Dactylis glomerata and Poa cita) obtained more nutrients when they grew together with proteas; this was a much stronger neighbour effect than was measured in Lolium perenne which is better adapted to high fertility soils. The findings illustrate both the functional compatibility and competition for plant nutrients in mixed-species rhizospheres. Species combinations substantially increased the acquisition of key elements from the soil nutrient pool.

Draft genome sequences of five Calonectria species from Eucalyptus plantations in China, Celoporthe dispersa, Sporothrix phasma and Alectoria sarmentosa

Draft genome sequences of five Calonectria species [including Calonectria aciculata, C. crousiana, C. fujianensis, C. honghensis and C. pseudoturangicola], Celoporthe dispersa, Sporothrix phasma and Alectoria sarmentosa are presented. Species of Calonectria are the causal agents of Eucalyptus leaf blight disease, threatening the growth and sustainability of Eucalyptus plantations in China. Celoporthe dispersa is the causal agent of stem canker in native Syzygium cordatum and exotic Tibouchina granulosa in South Africa. Sporothrix phasma was first discovered in the infructescences of Protea laurifolia and Protea neriifolia in South Africa. Alectoria sarmentosa is fruticose lichen belongs to the alectorioid clade of the family Parmeliaceae. The availability of these genome sequences will facilitate future studies on the systematics, population genetics, and genomics of these fungi.

Chemical synthesis and tyrosinase-inhibitory activity of isotachioside and its related glycosides

Isotachioside (1) and its related natural product 2 are isolated from Isotachis japonica and Protea neriifolia, respectively, and are categorized as analogs of arbutin (3), a tyrosinase inhibitor for practical use. Both of the natural products and several derivatives such as glucoside 4, xyloside 5, cellobioside 6, and maltoside 7 were synthesized via Schmidt glycosylation as a key step, and their tyrosinase inhibitory activity was evaluated. The half maximal inhibitory concentration (IC50) of 1–3 could not be determined even when the concentration was increased to 1000 μM. Contrastingly, glycosides 4–7, missing methyl and benzoyl groups, acted as tyrosinase inhibitors with IC50s of 417 μM, 852 μM, 623 μM, and 657 μM, respectively. Among these novel inhibitors, derivative 4 was the most potent, indicating that the structural combination of resorcinol and glucose was significant for inducing the inhibitory effect.

Rodents and baboons reduce seed cone production of Protea neriifolia

Rodents are important pollinators and seed predators of fynbos Proteaceae, but their role as florivores has received little attention. Chacma baboons (Papio hamadryas ursinus) are known to feed on Proteaceae inflorescences, however, their effect on plant reproduction has not been quantified. We recorded the extent of damage by rodents and baboons to inflorescences of the dominant shrub, Protea neriifolia, in 20×20m plots in the Jonkershoek Nature Reserve near Stellenbosch. Damage was distributed patchily across the landscape. Rodents damaged up to 23% of the inflorescences per plot by feeding on styles and nectar. We observed the striped mouse (Rhabdomys pumilio) climbing up plants to feed on inflorescences. Up to 14% of inflorescences in some plots were destroyed by rodents gnawing through inflorescence stems. Baboons damaged or destroyed 12% to 29% of inflorescences at three study sites, but did not forage at all in the three remaining study sites. Among plant individuals affected by baboons or rodents, a mean proportion of 0.49±0.31 (SD) of individuals' inflorescences were damaged or destroyed. Florivory by rodents and baboons can thus reduce the fecundity of P. neriifolia significantly. Protea inflorescences may be an important seasonal food source for certain rodents. In an evolutionary context, rodent florivory may have been an important selective force that caused certain Proteaceae species to shift to rodent pollination. Further work is needed to determine which rodent species feed on Protea inflorescences and whether rodent florivory is widespread in fynbos.

Protea hybrid ‘Carnival’ (P. compacta x P. neriifolia) expresses multiple copies of a LEAFY homologue involved in floral and vegetative development

Proteas are woody perennial plants that develop large, complex inflorescences which are popular as cut flowers. Four paralogous genes with sequence similarity to the meristem identity gene LEAFY (LFY) of Arabidopsis thaliana were identified in the Protea cultivar ‘Carnival’ (Protea compacta x Protea neriifolia). The deduced amino acid sequences of Protea LFY (ProLFY) paralogues displayed highly conserved N- and C-terminal regions comparable to that of other LFY proteins. Paralogous sequences shared 97–99% similarity at nucleotide and deduced amino acid levels. To determine if these ProLFY paralogues are involved in floral transition and development, three paralogues were heterologously expressed in A. thaliana Col-0 wild-type and lfy-2 mutant plants. These three paralogues were chosen as they had the greatest sequence dissimilarities which may suggest a different function. Expression of the ProLFY-WL4 paralogue rescued the low fertility of the lfy-2 mutant by restoring seed yield to wild-type levels, and resulted in the conversion of ‘leaf-like’ inflorescences to flowers with a wild-type appearance. ProLFY-WL4 expression levels during ‘Carnival’ meristem development confirmed a role for this paralogue in inflorescence development. The other two paralogues used in heterologous A. thaliana expression studies, ProLFY-L5 and ProLFY-D1, did not rescue fertility or the abnormal floral phenotype of lfy-2. However, transgenic plants developed either smaller leaves when expressing 35S::ProLFY-L5, or larger leaves when expressing 35S::ProLFY-D1, compared to the non-transgenic lfy-2 plants. Together these results suggest that ProLFY paralogues may be involved in both floral and vegetative development of Protea.

EVALUATION OF THE POTENTIAL FOR PROTEACEAE PRODUCTION IN NEW CALEDONIA

In 2003, while initiating an investigation into the potential of New Caledonia's native Proteaceae flora for ornamental purposes, we introduced 17 commercial taxa of South African and Australian Proteaceae as cut flowers and foliage in order to diversify the local floriculture industry. These taxa included Leucadendron 'Brook's Red', 'Inca Gold', 'Safari Sunset', 'Wilson's Wonder' and 'Long Tom'; Leucospermum 'Caroline', 'High Gold', 'Purple Gem', 'Scarlet Ribbon' and 'Sunrise'; Protea cynaroides and P. cynaroides 'Australis', Protea laurifolia 'Rose Mink', Protea neriifolia 'Silvertips' and Protea 'Pink Ice'; Serruria florida and Telopea 'Dawn Fire'. An experimental site with supposed adequate pedoclimatic conditions was identified in Northern New Caledonia. Soil analysis showed a silt loam texture with pH 5.6 and a very low level of 7 ppm for plant-available phosphorus. Average temperatures recorded throughout the trial were found to be the coolest (17-18°C) during the months of July and August, with the hottest (25-27°C) months being January and February. Preliminary results indicated that Telopea 'Dawn Fire', Serruria florida, Leucospermum 'Purple Gem' and L. 'Sunrise' were clearly not adapted to the growing conditions of the experimental site. In terms of yield, the Leucospermum cultivars, i.e. 'Scarlet Ribbon', 'Caroline' and 'High Gold' yielded the best results, whilst the two top performing Leucadendron cultivars were 'Inca Gold' and 'Safari Sunset'. Amongst the Protea species, P. neriifolia 'Silvertips' and P. cynaroides showed exceptional production potential.

Exogenous Cytokinin Induces “Out of Season” Flowering in Protea cv. Carnival

The cytokinin concentration in the xylem sap of Protea L. cv. Carnival (Protea compacta R. Br. × Protea neriifolia R. Br.) shoots was determined at regular intervals from 11 weeks before until 10 weeks after spring budbreak. Cytokinin levels were high during the early phases of spring shoot growth. Benzyladenine (BA) at 50, 250, or 500 mg·L−1 was applied to entire shoots on 22 Feb., 12 Apr., and 22 May 2001 (fall in the southern hemisphere) or only to terminal buds on 22 May 2001 at 500 mg·L−1. Most of the terminal buds sprouted and initiated an inflorescence when BA application at 500 mg·L−1 in May was directed only to terminal buds, whereas lower flowering percentages (0%–35%) were achieved when the entire shoot was treated. After whole shoots were treated with BA in Apr. 2001, between 5% and 45% floral reversion was observed. High flowering percentages of 87% to 93% were recorded when BA was applied at 500 mg·L−1 to the terminal bud in the dormant state or up to the stage when sprouting buds reached the green point development stage. Later applications were less effective, inducing 42% to 43% inflorescence initiation. The flowering time of BA-induced inflorescences was advanced by more than 2 months compared with flowers that initiated naturally on the spring flush.

Comparison of leaf susceptibility to enzymatic blackening in Protea neriifolia R. Br. and Leucospermum ‘Rachel’

Abstract Leaf susceptibility to blackening differs between Protea neriifolia R. Br. and Leucospermum ‘Rachel’ [( L. lineare × L. vestitum ) × L. glabrum ]; members from two different genera of the family Proteaceae. Protea leaf discs had a greater dry weight percentage and a higher protein and total phenolic content, than Leucospermum leaf discs. No significant difference was observed in ascorbic acid content in fresh leaf tissues of the two genera. Polyphenol oxidase (PPO) activity was high in Protea leaf homogenates with none being detected in Leucospermum leaf tissue at any pH. A significantly higher pH was observed in Protea leaf homogenate (pH 5.2) than in Leucospermum leaf homogenate (pH 4.4), with pH 5.2 being the optimum pH for PPO activity in Protea leaf. Mixing Protea leaf extract with Leucospermum leaf extract at pH 4.4–6.8 inhibited PPO activity, suggesting that Leucospermum leaf extract contained an unknown PPO inhibitor. The absence of leaf blackening in Leucospermum could be due to either or both the lower leaf homogenate pH and the presence of an inhibitor.

Are Protea populations seed limited? Implications for wildflower harvesting in Cape fynbos

Abstract Little is known about the extent to which plant population growth is limited by seed production. We studied two non‐sprouting Protea species, both entirely dependent on seeds for recruitment after fire, to determine how flower harvesting would affect the size of the next generation after burning. Five harvesting treatments (0, 25, 50, 75 and 100% inflorescence removal) were applied, each replicated four times in 10 × 10m plots. Seedbanks were censused before a late‐summer burn for each species and each replicate. The mean proportion of seeds surviving the burn until germination the following spring was 0.46 for Protea repens and 0.57 for Protea neriifolia. Of the seedlings that emerged, 90% and 55%, respectively, survived the first summer drought. Flower production in the 9 year old stand was strongly related to population density. Optimal plant densities for maximum flower production were estimated as 150 for P. repens and 70 for P. neriifolia. These target densities were greatly exceeded by seedling populations surviving the first summer drought in unharvested stands. If future density‐independent mortality is negligible, the excess represents that part of the seedbank that could have been harvested before the burn without influencing future flower production. We developed a simple static model for setting flower harvesting levels in these seed‐saturated populations. The predicted harvesting levels (50% of inflorescences in P. repens and 85% in P. neriifolia) were validated against the experimental harvests. We discuss the sensitivity of harvesting levels to variation in fecundity/density relationships, seed survival through a burn and seedling survival until flowering, and the implications for flower harvesting.

Source-Sink Relationship and Protea Postharvest Leaf Blackening

The inflorescence of Protea neriifolia B. Br. was two-thirds of the total cut floral stem fresh weight and significantly influenced blackening of the attached 20 to 30 leaves. Floral stems harvested at five developmental stages were characterized for inflorescence diameter, fresh and dry weights, respiration, and nectar production. Inflorescence diameter and fresh and dry weights increased from stage 1 (very tight bud) to stage 5 (bracts reflexed). Respiration rate was high in stages 1 and 3. Nectar production began at stage 4 (open, cylindrical flower) and increased from 2.7 to 9.8 ml per flower with 15% to 23.5% total soluble solids as the flower opened. Postharvest inflorescence diameter, respiration rate, and nectar production increased and leaf blackening decreased when floral stems were placed in 5% (w/v) sucrose solution. Application of 14C-sucrose to a leaf subtending the inflorescence lead to >50% of the radioactivity being found in the nectar within 24 hours. These data indicate that leaf blackening in protea is the result of depletion of carbohydrate by the inflorescence, and that this depletion is primarily due to the sugar demand for nectar production.

Selective predation onProtea Neriifolia(Proteaceae) seeds by small mammals

The ability of small mammals to select Protea neriifolia seeds containing embryos (full seeds) was examined. Full and empty seeds were glued to wooden boards and placed at three sites in young fynbos. Small mammals were able to select and remove significantly more full seeds than expected. Seed removal rates varied between the study sites but this was not related to the density of small mammals trapped at those sites. Selective feeding greatly increases the feeding efficiency of small mammals because 90% or more of the seed dispersed after fires may be empty.

Carbohydrate Metabolism and Possible Mechanisms of Leaf Blackening in Protea neriifolia under Dark Postharvest Conditions

During a 7-day dark postharvest period, Protea neriifolia R.Br. leaf blackening was significantly reduced on floral stems treated with a 24-h 20% sucrose pulse compared with continuous holding in a 0.5% sucrose vase solution or removal of the flowerhead. Leaf blackening on vegetative stems was similar to that on the 20% sucrose-pulsed floral stems. Leaf starch and sucrose concentration profiles demonstrated that stems with reduced leaf blackening maintained higher levels of those carbohydrates during the early postharvest period. Conversely, leaf starch and sucrose reserves were quickly depleted in stem treatments that resulted in early blackening symptoms. Starch concentrations in all treatments of stems dropped 70% to 82% within 24 h of harvest, suggesting that leaf blackening may be initiated during shipping. Ethylene production was not associated with leaf blackening in any treatment. Lipid peroxidation did not differ among floral treatments nor did it increase over the postharvest interval. Oxidized glutathione (GSSG) concentration increased only with the 20% pulsed stems and was not related to leaf blackening. After an initial decrease, leaf respiration rate was generally maintained regardless of treatment. Collectively, these data are consistent with the hypothesis that carbohydrate depletion is the initiating factor in leaf blackening and is accelerated by inflorescence sink demand. We suggest that membrane degradation does not necessarily precede leaf blackening.

Postharvest Leaf Blackening and Preharvest Carbohydrate Status in Three Protea Species

Protea neriifolia R. Br., P. susannae E.P. Phillips × compacta R. Br., and P. eximia (Salis. ex Knight) Fourcade cut flower stems were examined to determine the relationship between postharvest leaf blackening rate and preharvest carbohydrate status. Postharvest leaf blackening was highest (83% by day 4) in P. eximia floral stems, which had the lowest preharvest sucrose concentrations. In contrast, P. susannae × compacta had <5% leaf blackening by day 4 and the highest preharvest leaf sucrose concentrations. Starch concentrations were highest in P. neriifolia; however, leaf blackening was intermediate between P. susannae × compacta and P. eximia and reached 52% at day 4. Preharvest carbon-exchange rate and stomatal conductance in all three species were extremely low, despite high photosynthetically active radiation and apparent lack of water stress. Comparing preharvest carbohydrate profiles in vegetative and floral stems suggests that vegetative stems may have a sink-to-source transition zone between the second and third divisions, while most leaves on floral stems may have transferred carbohydates to source leaves at harvest. While preharvest floral stem sucrose concentrations can be linked to leaf blackening rate, the high starch reserves in P. neriifolia reduced leaf blackening little in this species. We conclude that leaf blackening may be related more to inflorescence sink demand after harvest and oxidative substrate availability than preharvest reserve carbohydrate concentrations in each species.

Effects of watering regime on growth and competitive ability of nursery-grown Cape fynbos and forest plants

Indigenous forests in the south-western Cape are restricted to sheltered habitats. Two forest species (Cunonia capensis L. and the pioneer Kiggelaria africana L.) and three fynbos species [Protea neriifolia R. Br., P. nitida Miller and P. repens (L.) L.] were individually cultivated under three levels of water availability to determine the influence of this factor on forest distribution. A diallel experiment with all combinations of pairs of C. capensis, K. africana, P. neriifolia and P. nitida was carried out under the same treatments to investigate competitive abilities. Growth of all species under individual cultivation improved with increased water availability. Morphological indicators of water stress (leaf size and specific leaf area) did not follow predicted patterns and diurnal measurements of conductance did not differentiate between forest and fynbos species. C. capensis showed high levels of mortality in the dry watering regime, but K. africana persisted in this treatment. The diallel experiment showed K. africana to be a superior competitor at all levels of water availability. C. capensis was an inferior competitor, especially in the dry treatment. P. nitida was an inferior competitor with high water availability, but watering regime had little effect on the competitive abilities of P. neriifolia. Forest development in xeric habitats may be precluded by the inability of forest species to establish in normal summer drought conditions. Once established under wet conditions, however, pioneer species such as K. africana may persist and develop.

TEMPERATURE IS A KEY REGULATOR OF GROWTH AND FLOWERING IN PROTEA NERIIFOLIA AND PROTEA CYNAROIDES

The strategy of this study was to determine the period of floral initiation for both species and then to determine the critical regulator(s) of flower initiation and floral development. Plants grown under different temperature regimes gave best shoot extension and flower initiation at temperatures with 10°C night and 15 to 25°C day. Field data from four locations showed a correlation of time of flower initiation and temperatures over the same range. Temperature is an important determinant of the vegetative flush period of both species. The stem diameter of all shoots is a consequence of the vegetative flush growth and in turn is well correlated with flower initiation. Plants given day temperatures of 20°C or above remain in the vegetative phase. Flower abortions in Protea neriifolia and reversions from floral to vegetative shoots in Protea cynaroidesresult from high day temperatures. Daylength was not found to be critical for flower initiation. A cool temperature period acts as a control to change shoots from the vegetative to reproductive phase.

PROTEA LEAF BLACKENING

Leaf blackening in Protea neriifolia R. Br. is influenced by sink demand and nectar production. Maximum nectar production occurred when the flower was in the cylindrical shape. C14-sucrose applied to a postharvest flower stem leaf moved preferentially into the nectar (65%). Darkness increased the rate of leaf blackening. Covering an individual leaf on a postharvest flower stem with aluminum foil lead to leaf blackening in 3 days while removing the inflorescence or girdling the stem just below the inflorescence prevented this leaf blackening. Girdling the stem around a leaf base and covering this leaf with foil resulted in leaf blackening in 5 days, but removal of the inflorescence influence did not prevent blackening. Sucrose 2.5% (w/v) in the vase solution prevented leaf blackening in both girdled and non-girdled leaves covered with foil. Polyphenol oxidase apparently plays an important role in protea leaf blackening. Leucospermum, another genera in the family of Proteaceae, did not show any PPO activity and did not blacken in the dark, while high PPO activity was detected in leaf extract of P. neriifolia.

INFLORESCENCE SINK DEMAND AND LEAF BLACKENING IN PROTEA NERIIFOLIA.

A major postharvest problem of Protea neriifolia is premature leaf blackening. Carbohydrate stress, due to floral sink demand, may lead to cellular disorganization and leaf blackening. Leaf blackening, nonstructural carbohydrates, ethylene, carbon exchange rates, stomatal conductance and lipid peroxidation were measured on leaves of vegetative and floral stems preharvest, and during a 7 day dark postharvest period. Postharvest treatments were: 0 or 0.5% sucrose in the vase solution, 20% sucrose pulse, or floral decapitation. Leaf blackening was significantly reduced in vegetative stems and floral stems in the 20% pulse treatment, in comparison to all other treatments. Ethylene production and lipid peroxidation were not associated with leaf blackening in any treatment and leaf respiration rates declined for all treatments over time. The magnitude and rate of leaf blackening was inversely related to leaf starch concentrations, with greatest carbohydrate depletion occurring within 24 h of harvest (by 75-85%). Leaf starch from the 20% pulse treatment increased by 300%, in contrast to declining starch concentrations in all other treatments. The data suggest that the flowerhead functions as the major sink for carbohydrate depletion leading to subsequent leaf blackening.

The role of photosynthesis and oxidative reactions in leaf blackening of Protea neriifolia R. Br. leaves

A series of experiments with Protea neriifolia R. Br. found evidence that leaf blackening is associated with the inhibition of photosynthesis and its resultant effect on oxidative metabolism. Leaf blackening was significantly reduced by constant illumination greater than 25 mol m −2 s −1. The light compensation point for P. Neriifolia leaves was estimated to be 24 mol m −2 s −1. Treatment of cut stems with 100 M 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of electron transport in Photosystem II, increased leaf blackening, indicating the necessity of active photosynthesis in the control of blackening. The nature of the oxidative processes resulting in blackening was examined. Dipping P. neriifolia stems in an anti-oxidant (diphenylamine, 1.5 mg 1 −1) resulted in a significant reduction in leaf blackening after 7 days. Storage in a low oxygen, controlled atmosphere (1% O 2, 5% CO 2) provided effective control against leaf blackening for up to 14 days at 25°C. It is proposed that leaf blackening in P. neriifolia leaves is inhibited by active photosynthesis, possibly through the production of carbohydrates as well as anti-oxidant or reducing compounds.

Effects of seed and seedling predation by small mammals on seedling recruitment of Protea neriifolia in Swartboskloof, Cape Province

Seed and seedling predation by small mammals, thought to be significant factors controlling the recruitment of Proteaceae in fynbos shrublands, were studied in a fynbos shrubland before and after a fire in March 1987. Seeds of Protea neriifolia R.Br. were planted inside and outside 14 mm mesh exclosures. The abundance of small mammals was recorded at two fynbos and five forest sites before the fire and at an additional forest and fynbos site after the fire. Seed predation reduced seedling recruitment from seeds planted in March 1986 in mature fynbos, but the reduction was significant only at the site with the highest abundance of small mammals. Seed predation did not significantly reduce seedling recruitment from seed planted in July, August and September 1986 in mature fynbos. The primary cause of seedling mortality before the fire was wilting, presumably owing to moisture stress. After the fire small mammal abundance decreased in burnt fynbos and increased in unburnt forest refuges until eight months after the fire when it increased again in the fynbos to a maximum of 41 animals per 100 trapnights two years after the fire. Seedling predation by small mammals had a limited impact after the fire probably because their numbers dropped soon after the fire. The effects of seed predation did not decrease with increasing distance from a forest refuge. Fungal pathogens and herbivory by insects were the primary causes of seedling mortality after the fire. Small mammal abundance in mature fynbos 25–30 years after a fire may have been too low to prevent the recruitment of a second cohort of P. neriifolia seedlings.

The effects of exposure to different environments on the viability of Protea neriifolia seeds

The effects of exposure to different environments on the viability of Protea neriifolia seeds