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  • Author or Editor: David Graper x
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Non flowering Alstroemeria `Regina' plants were divided into aerial components: stems and apical and basal leaves or underground components: rhizome, storage roots, stele and fibrous roots. Samples were collected from distal and proximal ends of the rhizome to allow comparisons between structures of different ages. Ethanol soluble sugars were extracted and measured using HPLC. Starch was degraded to glucose using amyloglucosidase and measured.

There were no age differences in the starch, total soluble sugar (TSUGAR) or total soluble carbohydrates (TCHO) in the rhizome or aerial portions of the plant. There was a preferential partitioning of starch, sucrose, TSUGAR and TCHO to underground plant parts. The storage roots were the primary sink for the stored carbohydrates. Stems contained large concentration of glucose while fructose was found in storage roots and old stems. Sucrose was found primarily in old steles and storage roots. Starch was partitioned almost exclusively into the storage roots with no difference due to age of the storage root. Up to 42% of the TCHO in the old storage roots was composed of a carbohydrate which co-chromatogramed with melezitose using HPLC.

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Petunia `Red Flash' seedlings were grown under HPS (175 μmol m-2 s-1) photoperiod treatments of 10, 12, 14 or 16 hr at 20C soil temperature in a shaded glasshouse where the maximum peak PPF was reduced to 150 μmolm-2s-1. Seedling were transplanted after they had unfolded a specific number of leaves and grown under natural days or placed under photoperiod treatments which consisted of an 8 hr natural day with incandescent day extension treatments of 1 to 6 hours.

A 16 hr HPS treatment decreased the days to transplant (DTT) by more than 4 days and reduced the days from transplant to flower (DTF) by more than 5 days. The total reduction in days from sowing to flower (DSTF) was at least 8 days. When compared to unlighted controls, the reduction in DSTF was 26 days. The longer the seedlings remained under the HPS treatments, the shorter the DTF and DSTF. Premature shifting of plants to natural days resulted in up to a 9 day delay in DSTF. At photoperiods greater than 13 hr, the number of nodes subtending the inflorescence becomes constant regardless of number of leaves at transplant.

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Petunia `Red Flash' seedling were grown under HPS (175 μmolm-2 s-1) photoperiod treatments of 10, 12, 14 or 16 hr at 20C soil temperature in a shaded glasshouse where the maximum peak PPF was reduced to 150 μmolm-2s-1. Seedling dry weight and individual leaf area were determined daily. The photosynthetic rate was determined when seedlings reached the second true leaf stage.

The dry weight response to increasing photoperiod durations was cubic with a peak at 14 hr. Seedling dry weight increased slowly during days 5 through 10 then increased rapidly during the next 7 to 10 days. This increase coincided with the unfolding of leaves one through four. The total leaf area showed a cubic response to the photoperiod treatments. The leaf area increased slowly then began an exponential increase after day 10. The photosynthetic rate per gram dry weight was increased by the 10 hr photoperiod treatment when compared to the 16 hr treatment. The increased photosynthetic rate was not observed when the data was calculated on a fresh weight or leaf area basis.

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The increase in photosynthetic photon flux (PPF) and plant temperature associated with supplemental high pressure sodium (HPS) irradiation were investigated during Petunia × hybrids Villm. `Red Flash' seedling development. Seedlings were treated for 14 days following emergence or 5 days after the first true leaf had expanded to 1 mm. Treatments consisted of continuous infrared (IR) radiation (Ambient + IR), ambient conditions with spill-over radiation from adjacent treatments (Ambient - IR), root zone heating to 19.5C (RZ Heat), continuous HPS irradiation at 167 μmol·s-1.m-2 PPF (HPS + IR) or continuous HPS irradiation at 167 μmol-1·m-2 PPF filtered through a water bath to remove IR (HPS - IR). Linear regression of natural log-transformed fresh weights indicated that increasing ambient PPF 53% and elevating plant temperature 4.3C (HPS + IR) increased seedling relative growth rate (RGR) by 45% compared with the control (Ambient - IR). Elevating plant temperature with + IR by 4.8C without supplementing PPF (Ambient + IR) increased RGR by 31% but failed to increase fresh weight (FW) above controls and resulted in etiolated plants that were unsuitable for transplanting. Once plants were removed from supplemental treatment and returned to ambient conditions, RGR for all treatments was similar. The increased FW promoted by IR and HPS treatments was maintained for up to 7 days after treatment. Therefore, the increased seedling growth responses observed with HPS treatment were due primarily to an increase in RGR during HPS treatment that is not sustained beyond treatment.

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Petunia × hybrida Villm. `Red Flash' plants received either 10 or 20 mol·day-1 photosynthetic photon flux (PPF) in growth chambers at: 175 μmol·m-2·s-1 for 16 hours, 350 μmol·m-2·s-1 for 8 or 16 hours, or 350 μmol·m-2 s-1 for 8 hours plus 8 hours of incandescent photoperiod extension (5 μmol·m-2·s-1 PPF). The irradiation components of peak, total, and duration were examined. Doubling total PPF increased total carbohydrate (CHO) production by 60%, seedling dry weight (DW) by 30%, rate of seedling growth by 25%, and acid invertase activity by 50% compared to the other treatments, once the seedlings had reached the two-leaf stage. Seedlings receiving 20 mol·day-1 PPF partitioned 14% more CHO into ethanol soluble sugars rather than starch, which may explain the increase in relative growth rate observed with supplemental irradiance treatments. Extending the photoperiod for 8 hours with 5 μmol·m-2·s-1 PPF reduced total CHO production by 50% compared to the same treatment without photoperiodic lighting. Treatment with 350 μmol·m-2·s-1 for 8 hours resulted in the highest O2 evolution (8.8 μmol O2/min per dm2). Increasing the photoperiod from 8 to 16 hours gave the lowest rate of O2 evolution (4.5 μmol O2/min per dm2). Previous reports of the importance of photosynthetic period in controlling partitioning between starch and sugars may have simply observed a decreasing rate of starch accumulation due to increased total PPF.

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