add PlantMaterialAndGrowthConditions protocol

studies/NicotianaBenthamiana/protocols/PlantMaterialAndGrowthConditions.md

+## PlantMaterialAndGrowthConditions
+Seeds of *N. benthamiana* wild-type lines were sown on soil and grown for 3 weeks in the greenhouse under long-day conditions (day/night cycle of 16/8 h, 22–25 °C, light intensity of ∼140 μmol·m−2·s−1, maximal humidity of 60%).
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