Insights into the profiling changes of amino acid content in an albino mutant (Camellia sinensis cv. Huangshanbaicha) during the albinostic stage

Abstract Albino cultivars of Camellia sinensis are widely cultivated in China for producing a unique type of green teas with high abundance of free amino acid. However, the underlying mechanism of enhanced amino acids metabolism in albino leaves at different growth stages is still elusive. This study examined the profile changes of amino acids in the albino tea cultivar ‘Huangshanbaicha’ (HSBC), compared with the normal green cultivar ‘Huangshanzhong’ (HSZ). High-performance liquid chromatography (HPLC) was employed to assess the free amino acid content in the current shoots grown in spring from albinostic to regreening stages. Transcript levels of the key genes involved in amino acid metabolism, and transportation were also quantified by qRT-PCR. The results indicated that the contents of free amino acids in four developmental stages of the ‘HSBC’ current shoots were in descending order: albinostic stage (S1) > bud stage (S0) > albescent stage (S2) > re-greening stage (S4). The total amino acid content at S1 stage reached to 7.10%, 1.8 and 2.6 times higher than the corresponding levels at S0 and S4, respectively. Moreover, from S0 to S4, the leaf composition of amino acids did not significantly change. Theanine, a characteristic amino acid of the tea plant, accounted for the largest proportion of 61.3%–70.2% relative to the total amount of all amino acids. The second most abundant component, glutamate, had a proportion far lower than that of theanine and varied between 6.3% and 15.7%. Expression levels of the genes involved in theanine synthesis were significantly higher in ‘HSBC’ than in ‘HSZ’, suggesting enhanced ability of theanine synthesis was appeared in ‘HSBC’ at the albinostic stage. Moreover, the transcript levels of amino acid transporter genes in ‘HSBC’ were significantly lower than those in ‘HSZ’. Together, these findings demonstrated that the significantly increased amino acid content in the leaves of ‘HSBC’ during the albinostic stage, which might be partially resulted from enhanced ability of theanine synthesis and reduced capability amino acids transport in the leaves of ‘HSBC’ tea plants during the albinostic stage.