The Control of Carbon Translocation in a Sea Anemone-Dinoflagellate Symbiosis from New Zealand

<p>Anthopleura aureoradiata, a common sea anemone of New Zealand's intertidal mudflats and rocky shores, hosts symbiotic dinoflagellates of the genus Symbiodinium. This study investigated the control of photosynthetic carbon translocation in this symbiosis, and in particular the presence and operation of socalled 'host release factor' (HRF). Evidence for HRF exists in a number other algalinvertebrate symbioses, where tissue extracts of the host stimulate carbon release by isolated algal symbionts. However, its identity remains elusive and it has never been studied before in A. aureoradiata. Translocation of photosynthetically-fixed carbon in the intact symbiosis and in the presence of host tissue extract was measured using a 14C label. Zooxanthellae in the intact symbiosis released around 40% of their photosynthetically-fixed carbon to the anemone. Isolated zooxanthellae, however, translocated only 8%, even less than the amount of photosynthate liberated by zooxanthellae in FSW alone (11%). Photosynthetic rates per algal cell were similar in the intact symbiosis and both host homogenate and FSW incubations, meaning that the total amount of photosynthetically-fixed carbon released (in pg C/cell/h) by the zooxanthellae in these different situations reflected the %translocation values. Given the failure of homologous zooxanthellae (i.e. those from A. aureoradiata) to respond to homogenized host tissue, it was tested whether zooxanthellae from other host species (i.e. cultured heterologous algae) responded. Heterologous zooxanthellae representing 5 clades (A-E) of Symbiodinium were incubated in host tissue homogenate and photosynthate release again measured with 14C. The %translocation varied from 12-51% in A. aureoradiata homogenate and 17-67% in FSW, again suggesting a lack of an active HRF in the homogenized tissues of this sea anemone. Photosynthetic rates amongst the different heterologous algae also varied widely with, for instance, freshly isolated zooxanthellae from A. aureoradiata having 6-fold higher photosynthetic rates than cultured algae from the same clade (clade A). The zooxanthellae of A. aureoradiata are known to be N-sufficient in the field, and studies with other species have demonstrated that N-deficient zooxanthellae release more photosynthate in response to HRF than do N-sufficient ones. Therefore, induction of an HRF effect was attempted by starving sea anemones, and hence their zooxanthellae, prior to incubation of freshly isolated zooxanthellae in homogenized tissue. However, even after 8 weeks of starvation, the zooxanthellae showed no signs of N-deficiency (as indicated by the extent to which ammonium enhanced the rate of dark 14C fixation), meaning that the relationship with HRF activity could not be examined. The ability of these temperate zooxanthellae to maintain their Nsufficiency, even after relatively long periods of food deprivation, may indicate a lower reliance on host feeding for nitrogen than is seen in tropical zooxanthellae, or a greater capacity to use internal stores of nitrogen. The lack of photosynthate release by both homologous and heterologous zooxanthellae in host homogenate, as opposed to substantial carbon released in the intact symbiosis, suggests that control of carbon translocation in A. aureoradiata is not related to the activity of an HRF; alternatively, if an HRF is present, its activity is hindered when the symbiosis is disrupted. Further study is needed to determine what is responsible for the control of photosynthate translocation in the A. aureoradiata-Symbiodinium symbiosis.</p>

The Control of Carbon Translocation in a Sea Anemone-Dinoflagellate Symbiosis from New Zealand

<p>Anthopleura aureoradiata, a common sea anemone of New Zealand's intertidal mudflats and rocky shores, hosts symbiotic dinoflagellates of the genus Symbiodinium. This study investigated the control of photosynthetic carbon translocation in this symbiosis, and in particular the presence and operation of socalled 'host release factor' (HRF). Evidence for HRF exists in a number other algalinvertebrate symbioses, where tissue extracts of the host stimulate carbon release by isolated algal symbionts. However, its identity remains elusive and it has never been studied before in A. aureoradiata. Translocation of photosynthetically-fixed carbon in the intact symbiosis and in the presence of host tissue extract was measured using a 14C label. Zooxanthellae in the intact symbiosis released around 40% of their photosynthetically-fixed carbon to the anemone. Isolated zooxanthellae, however, translocated only 8%, even less than the amount of photosynthate liberated by zooxanthellae in FSW alone (11%). Photosynthetic rates per algal cell were similar in the intact symbiosis and both host homogenate and FSW incubations, meaning that the total amount of photosynthetically-fixed carbon released (in pg C/cell/h) by the zooxanthellae in these different situations reflected the %translocation values. Given the failure of homologous zooxanthellae (i.e. those from A. aureoradiata) to respond to homogenized host tissue, it was tested whether zooxanthellae from other host species (i.e. cultured heterologous algae) responded. Heterologous zooxanthellae representing 5 clades (A-E) of Symbiodinium were incubated in host tissue homogenate and photosynthate release again measured with 14C. The %translocation varied from 12-51% in A. aureoradiata homogenate and 17-67% in FSW, again suggesting a lack of an active HRF in the homogenized tissues of this sea anemone. Photosynthetic rates amongst the different heterologous algae also varied widely with, for instance, freshly isolated zooxanthellae from A. aureoradiata having 6-fold higher photosynthetic rates than cultured algae from the same clade (clade A). The zooxanthellae of A. aureoradiata are known to be N-sufficient in the field, and studies with other species have demonstrated that N-deficient zooxanthellae release more photosynthate in response to HRF than do N-sufficient ones. Therefore, induction of an HRF effect was attempted by starving sea anemones, and hence their zooxanthellae, prior to incubation of freshly isolated zooxanthellae in homogenized tissue. However, even after 8 weeks of starvation, the zooxanthellae showed no signs of N-deficiency (as indicated by the extent to which ammonium enhanced the rate of dark 14C fixation), meaning that the relationship with HRF activity could not be examined. The ability of these temperate zooxanthellae to maintain their Nsufficiency, even after relatively long periods of food deprivation, may indicate a lower reliance on host feeding for nitrogen than is seen in tropical zooxanthellae, or a greater capacity to use internal stores of nitrogen. The lack of photosynthate release by both homologous and heterologous zooxanthellae in host homogenate, as opposed to substantial carbon released in the intact symbiosis, suggests that control of carbon translocation in A. aureoradiata is not related to the activity of an HRF; alternatively, if an HRF is present, its activity is hindered when the symbiosis is disrupted. Further study is needed to determine what is responsible for the control of photosynthate translocation in the A. aureoradiata-Symbiodinium symbiosis.</p>

Photoselective Nets Alter Apple Canopy Air Temperature and Carbon Translocation during Dormancy and Budbreak

Photoselective nets were used to examine apple shoot physiology during dormancy and budbreak. Two trials were conducted: one in the field and one in controlled conditions. In the first, three colored nets (red, blue, and white, shading 20%) covered sections of single trees, leaving an empty portion as control, from December to April. The white net increased canopy air temperature compared with the blue one. Differences were found in carbohydrate seasonal patterns; however, it appeared that soil temperature had higher impacts on sugar movement in the trees. No differences were found in bud phenology. In the second trial, cuttings were placed in boxes constructed with the same-colored nets and monitored from the end of February to April. Results showed differences in phenology and carbohydrate translocation. The white box hastened bloom and its cuttings had higher amounts of carbohydrates at the end of the trial. On the contrary, the blue box delayed bloom while resources were still being consumed and its cuttings had the lowest amounts of reserves at the end of the trial. These results add new insights on apple physiology under different light spectra and commercial applications should not be excluded for improving crop management.

Endogenous translocation patterns of current photosynthate in post-transplant Quercus rubra seedlings

Variability between individuals can cause error in plant physiology studies when measurements or treatments occur on a chronological basis. Thus, plant growth indices such as the Quercus morphological index (QMI) were developed, enabling distinctions between exogenous treatment effects and endogenous ontological effects. Few studies have examined post-transplant northern red oak (Quercus rubra L.) seedling physiology in relation to the QMI. We used 14CO2 to label current photosynthate of post-transplant northern red oak seedlings during the first flush to assess endogenous patterns of current photosynthate translocation. Carbon translocation patterns relative to QMI growth stages of post-transplant seedlings resembled those described in pre-transplant seedlings, with expanding leaves and shoots retaining the majority of current photosynthate early in the flush, followed by increases in downward translocation to both new and old roots during the lag stage, when active aboveground growth ceased for the flush. Early post-transplant growth of new shoots relied heavily on stored carbohydrates, and old shoots demonstrated negligible sink strength for current photosynthate throughout the experiment. Our findings emphasize the importance of stored carbohydrates for early post-transplant growth and suggest that QMI-based observations regarding carbohydrate translocation patterns of pre-transplant seedlings in this species remain largely valid for post-transplant seedlings.

Meta-analysis reveals host-dependent nitrogen recycling as a mechanism of symbiont control in Aiptasia

The metabolic symbiosis with photosynthetic algae of the genus Symbiodinium allows corals to thrive in the oligotrophic environments of tropical seas. Many aspects of this relationship have been investigated using transcriptomic analyses in the emerging model organism Aiptasia. However, previous studies identified thousands of putatively symbiosis-related genes, making it difficult to disentangle symbiosis-induced responses from undesired experimental parameters. Using a meta-analysis approach, we identified a core set of 731 high-confidence symbiosis-associated genes that reveal host-dependent recycling of waste ammonium and amino acid synthesis as central processes in this relationship. Combining transcriptomic and metabolomic analyses, we show that symbiont-derived carbon enables host recycling of ammonium into nonessential amino acids. We propose that this provides a regulatory mechanism to control symbiont growth through a carbon-dependent negative feedback of nitrogen availability to the symbiont. The dependence of this mechanism on symbiont-derived carbon highlights the susceptibility of this symbiosis to changes in carbon translocation, as imposed by environmental stress.

Experimentally Induced Bleaching in the Sea Anemone Exaiptasia Supports Glucose as a Main Metabolite Associated with Its Symbiosis

Our current understanding of carbon exchange between partners in the Symbiodinium-cnidarian symbioses is still limited, even though studies employing carbon isotopes have made us aware of the metabolic complexity of this exchange. We examined glycerol and glucose metabolism to better understand how photosynthates are exchanged between host and symbiont. The levels of these metabolites were compared between symbiotic and bleached Exaiptasia pallida anemones, assaying enzymes directly involved in their metabolism. We measured a significant decrease of glucose levels in bleached animals but a significant increase in glycerol and G3P pools, suggesting that bleached animals degrade lipids to compensate for the loss of symbionts and seem to rely on symbiotic glucose. The lower glycerol 3-phosphate dehydrogenase but higher glucose 6-phosphate dehydrogenase specific activities measured in bleached animals agree with a metabolic deficit mainly due to the loss of glucose from the ruptured symbiosis. These results corroborate previous observations on carbon translocation from symbiont to host in the sea anemone Exaiptasia, where glucose was proposed as a main translocated metabolite. To better understand photosynthate translocation and its regulation, additional research with other symbiotic cnidarians is needed, in particular, those with calcium carbonate skeletons.