Since we are going to study calcium waves, you cannot let your sample dry. I guess you can prepare a coated coverslip with something where your polen will adhere. Then you can put this into a chamber, label with Fluo4 am and then stimulate with your desired solution or just observe. Another option is to make a thick sucrose solution with your polen samples and take it straight to imaging, after labeling with fluo 4. I’ll look up for a paper and we’ll send you right away