The quantitative effects of temperature and light intensity on accumulation of phenolics were examined on greenhouse-grown plants of Hypericum perforatum L. Plants were grown in a greenhouse separated into two parts: shaded by 50% transparent polyethylene cover and un-shaded. Temperature values and light intensities were measured daily during the experiment, while plants were harvested weekly for HPLC analyses. Multi regression analyses were performed to describe the quantitative effects of temperature and light intensity on phenolics accumulation. According to the results, increases in temperatures from 24°C to 32°C and light intensities from 803.4 µMm-2 s-1 to 1618.6 µMm-2 s-1 resulted in a continuous increase in amentoflavone, apigenin-7-glucoside, cholorogenic acid, hyperoside, kaempferol, rutin, quercetin and quercitrin contents. The relationships between temperature, light intensity and phenolics accumulation were formulized as P= [a + (b 1 x t) + (b 2 x l) + [b 3 x(t x l)]] equition, where P is the content of the corresponding phenolic, t temperature (°C), l light intensity (µMm-2 s-1) and a, b 1 , b 2 and b 3 the coefficients of the produced equation. The regression coefficient (R 2) value for amentoflavone was 0.84, for apigenin-7glucoside 0.87, for cholorogenic acid 0.83, for hyperoside 0.95, for kaempferol 0.76, for rutin 0.70, for quercetin-0.93, and for quercitrin-0.86. All R 2 values and standard errors of the equations were found to be significant at the p<0.001 level. The mathematical models produced in the present study could be applied by Hypericum researchers as useful tools for the prediction of phenolics content instead of routine chemical analyses.

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Changes in plant growth viz. leaf area, leaf weight ratio, root weight ratio, dry leaf weight, dry root weight, total plant dry weight, specific leaf area, leaf thickness, leaf area ratio, net assimilation rate and relative growth rate due to the effects of environmental conditions such as temperature and light intensity were described by plant growth models. All equations produced for growth parameters were affected by light intensity and temperature. From multi-regression analysis, close relationships were found between actual and predicted growth parameters. The regression coefficients (r²) of the equations for growth parameters varied from 0.95 to 0.99 for cultivar Ecdogelb and 0.83 to 0.99 for cultivar Ecdorot, respectively.

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