Natural Variations and Dynamic Changes of Nitrogen Indices throughout Growing Seasons for Twenty Tea Plant (Camellia sinensis) Varieties

Assessing the health risks of heavy metals and seasonal minerals fluctuations in Camellia sinensis cultivars during their growth seasons

The risk assessment of heavy metals in tea is extremely imperative for the health of tea consumers. However, the effects of varietal variations and seasonal fluctuations on heavy metals and minerals in tea plants remain unclear. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to evaluate the contents of aluminum (Al), manganese (Mn), magnesium (Mg), boron (B), calcium (Ca), copper (Cu), cobalt (Co), iron (Fe), sodium (Na), zinc (Zn), arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), and antimony (Sb) in the two categories of young leaves (YL) and mature leaves (ML) of tea (Camellia sinensis) cultivars throughout the growing seasons. The results showed significant variations in the contents of the investigated nutrients both among the different cultivars and growing seasons as well. Furthermore, the average concentrations of Al, Mn, Mg, B, Ca, Cu, Co, Fe, Na, Zn, As, Cd, Cr, Ni, and Sb in YL ranged, from 671.58-2209.12, 1260.58-1902.21, 2290.56-2995.36, 91.18-164.68, 821.95-5708.20, 2.55-3.80, 3.96-25.22, 37.95-202.84, 81.79-205.05, 27.10-69.67, 0.028-0.053, 0.065-0.127, 2.40-3.73, 10.57-12.64, 0.11-0.14 mg kg-1, respectively. In ML, the concentrations were 2626.41-7834.60, 3980.82-6473.64, 3335.38-4537.48, 327.33-501.70, 9619.89-13153.68, 4.23-8.18, 17.23-34.20, 329.39-567.19, 145.36-248.69, 40.50-81.42, 0.089-0.169, 0.23-0.27, 5.24-7.89, 18.51-23.97, 0.15-0.19 mg kg-1, respectively. The contents of all analyzed nutrients were found to be higher in ML than in YL. Target hazard quotients (THQ) of As, Cd, Cr, Ni, and Sb, as well as the hazard index (HI), were all less than one, suggesting no risk to human health via tea consumption. This research might provide the groundwork for essential minerals recommendations, as well as a better understanding and management of heavy metal risks in tea.

Overexpression of CsATG3a improves tolerance to nitrogen deficiency and increases nitrogen use efficiency in arabidopsis

Nitrogen (N) is a major nutrition element for tea plant. However, application of high levels of N negatively causes environmental problems. Therefore, improved N use efficiency (NUE) of tea plant will be highly desirable and crucial for sustainable tea cultivation. Autophagy plays a central role in N recycling and holds potential to improve N utilization, and many AuTophaGy-related genes (ATGs) are involved in the autophagy process. Here, CsATG3a was identified from Camellia sinensis, and the functions involved in N utilization was characterized in arabidopsis (Arabidopsis thaliana). The transcript level of CsATG3a in tea leaves increases with their maturity. Relative to the wild type (WT) arabidopsis, two CsATG3a-overexpressing (CsATG3a-OE) lines exhibited improved vegetative growth, delayed reproductive stage, and upregulated expression of AtATGs (AtATG3, AtATG5 and AtATG8b) in a low N (LN) hydroponic condition. The expression levels of AtNRT1.1, AtNRT2.1, AtNRT2.2, AtAMT1.1 and AtAMT1.3 for N uptake and transport in roots were all significantly higher in CsATG3a-OE lines compared with those in the WT under LN. Meanwhile, the overexpression of CsATG3a in arabidopsis also increased N and dry matter allocation into both rosette leaves and roots under LN. Additionally, compared with WT, improved HI (harvest index), NHI (N harvest index), NUtE (N utilization efficiency) and NUE (N use efficiency) of CsATG3a-OE lines were further confirmed in a low-N soil cultured experiment. Together, these results concluded that CsATG3a is involved in N recycling and enhances tolerance to LN, indicating that CsATG3a holds potential promise to improve NUE in tea plant.

CsATG101 Delays Growth and Accelerates Senescence Response to Low Nitrogen Stress in Arabidopsis thaliana

For tea plants, nitrogen (N) is a foundational element and large quantities of N are required during periods of roundly vigorous growth. However, the fluctuation of N in the tea garden could not always meet the dynamic demand of the tea plants. Autophagy, an intracellular degradation process for materials recycling in eukaryotes, plays an important role in nutrient remobilization upon stressful conditions and leaf senescence. Studies have proven that numerous autophagy-related genes (ATGs) are involved in N utilization efficiency in Arabidopsis thaliana and other species. Here, we identified an ATG gene, CsATG101, and characterized the potential functions in response to N in A. thaliana. The expression patterns of CsATG101 in four categories of aging gradient leaves among 24 tea cultivars indicated that autophagy mainly occurred in mature leaves at a relatively high level. Further, the in planta heterologous expression of CsATG101 in A. thaliana was employed to investigate the response of CsATG101 to low N stress. The results illustrated a delayed transition from vegetative to reproductive growth under normal N conditions, while premature senescence under N deficient conditions in transgenic plants vs. the wild type. The expression profiles of 12 AtATGs confirmed the autophagy process, especially in mature leaves of transgenic plants. Also, the relatively high expression levels for AtAAP1, AtLHT1, AtGLN1;1, and AtNIA1 in mature leaves illustrated that the mature leaves act as the source leaves in transgenic plants. Altogether, the findings demonstrated that CsATG101 is a candidate gene for improving annual fresh tea leaves yield under both deficient and sufficient N conditions via the autophagy process.